suggests people at a rock concert (or an open mic at the corner sandwich shop) are definitely there to worship, they’re just there to worship something or someone besides Jesus. Based on that, the expectation for us as worship leaders should be no different. Some people are at church to worship Jesus, some aren’t. It all depends on how we can best direct peoples hearts towards Him. I think at a sandwich shop this is hard to do and may not be very easy to accomplish from behind the mic. But if you’re good, or you connect with some folks while you’re there, you may build relationships or conversations which allow you to address people and their gods directly rather than simply trying to preach through your songs - though that could work…
I also had some thoughts on what you said about musicians inserting ‘fancy’ things during corporate worship. I actually got asked question pertaining to this subject at a conference my church recently had, and these thoughts are based less on a specific passage of scripture and more on combined ideas I’ve gotten from things such as Acts 17Acts 17
[17:1]Now when they had passed through Amphipolis and
Apollonia, they came to Thessalonica, where there was a
synagogue of the Jews. [2]And Paul went in, as was his
custom, and on three Sabbath days he reasoned with them
from the Scriptures, [3]explaining and proving that it was
necessary for the Christ to suffer and to rise from the
dead, and saying, "This Jesus, whom I proclaim to you, is
the Christ." [4]And some of them were persuaded and joined
Paul and Silas, as did a great many of the devout Greeks
and not a few of the leading women. [5]But the Jews were
jealous, and taking some wicked men of the rabble, they
formed a mob, set the city in an uproar, and attacked the
house of Jason, seeking to bring them out to the crowd.
[6]And when they could not find them, they dragged Jason
and some of the brothers before the city authorities,
shouting, "These men who have turned the world upside down
have come here also, [7]and Jason has received them, and
they are all acting against the decrees of Caesar, saying
that there is another king, Jesus." [8]And the people and
the city authorities were disturbed when they heard these
things. [9]And when they had taken money as security from
Jason and the rest, they let them go.
[10]The brothers immediately sent Paul and Silas away by
night to Berea, and when they arrived they went into the
Jewish synagogue. [11]Now these Jews were more noble than
those in Thessalonica; they received the word with all
eagerness, examining the Scriptures daily to see if these
things were so. [12]Many of them therefore believed, with
not a few Greek women of high standing as well as men.
[13]But when the Jews from Thessalonica learned that the
word of God was proclaimed by Paul at Berea also, they came
there too, agitating and stirring up the crowds. [14]Then
the brothers immediately sent Paul off on his way to the
sea, but Silas and Timothy remained there. [15]Those who
conducted Paul brought him as far as Athens, and after
receiving a command for Silas and Timothy to come to him as
soon as possible, they departed.
[16]Now while Paul was waiting for them at Athens, his
spirit was provoked within him as he saw that the city was
full of idols. [17]So he reasoned in the synagogue with the
Jews and the devout persons, and in the marketplace every
day with those who happened to be there. [18]Some of the
Epicurean and Stoic philosophers also conversed with him.
And some said, "What does this babbler wish to say?" Others
said, "He seems to be a preacher of foreign divinities"--
because he was preaching Jesus and the resurrection.
[19]And they took him and brought him to the Areopagus,
saying, "May we know what this new teaching is that you are
presenting? [20]For you bring some strange things to our
ears. We wish to know therefore what these things mean."
[21]Now all the Athenians and the foreigners who lived
there would spend their time in nothing except telling or
hearing something new.
[22]So Paul, standing in the midst of the Areopagus,
said: "Men of Athens, I perceive that in every way you are
very religious. [23]For as I passed along and observed the
objects of your worship, I found also an altar with this
inscription, 'To the unknown god.' What therefore you
worship as unknown, this I proclaim to you. [24]The God who
made the world and everything in it, being Lord of heaven
and earth, does not live in temples made by man, [25]nor is
he served by human hands, as though he needed anything,
since he himself gives to all mankind life and breath and
everything. [26]And he made from one man every nation of
mankind to live on all the face of the earth, having
determined allotted periods and the boundaries of their
dwelling place, [27]that they should seek God, in the hope
that they might feel their way toward him and find him. Yet
he is actually not far from each one of us, [28]for
"'In him we live and move and have our being';
as even some of your own poets have said,
"'For we are indeed his offspring.'
[29]Being then God's offspring, we ought not to think that
the divine being is like gold or silver or stone, an image
formed by the art and imagination of man. [30]The times of
ignorance God overlooked, but now he commands all people
everywhere to repent, [31]because he has fixed a day on
which he will judge the world in righteousness by a man
whom he has appointed; and of this he has given assurance
to all by raising him from the dead."
[32]Now when they heard of the resurrection of the dead,
some mocked. But others said, "We will hear you again about
this." [33]So Paul went out from their midst. [34]But some
men joined him and believed, among whom also were Dionysius
the Areopagite and a woman named Damaris and others with
them. (ESV)

and 1 Corinthians 9:18-231 Corinthians 9:18-23
[18]What then is my reward? That in my preaching I may
present the gospel free of charge, so as not to make full
use of my right in the gospel.
[19]For though I am free from all, I have made myself a
servant to all, that I might win more of them. [20]To the
Jews I became as a Jew, in order to win Jews. To those
under the law I became as one under the law (though not
being myself under the law) that I might win those under
the law. [21]To those outside the law I became as one
outside the law (not being outside the law of God but under
the law of Christ) that I might win those outside the law.
[22]To the weak I became weak, that I might win the weak. I
have become all things to all people, that by all means I
might save some. [23]I do it all for the sake of the
gospel, that I may share with them in its blessings. (ESV)

…
My general thought is that people can play in a church context or a ’secular’ context and be in it for their glory or Jesus’ glory - even if they’re a Christian. In the context of corporate worship, I ALWAYS enjoy God’s blessing of music more (and am therefore more inclined to worship Him through it) when excellent musicianship is displayed. This could be a shredding guitar solo or even a subtle drum grove that doesn’t stand out. For me, when the musician’s heart is in the right place, they become a mere vessel for God to display His glory through them rather than a distraction from me being ‘able to worship’.
So, that’s my thoughts - sorry to be so long-winded. I would love to see what other people think of that (especially Bob!).
Peace