Warwickshire libraries did something similar in Rugby a few years ago. Can't remember the bands now, but nothing was quite my taste so I didn't go.
Just my view, but I think those gigs just didn't work other than a basic 'how many people visited our building' exercise. My mate goes (or rather, went, he doesn't now because his work gets disrupted by bands!) into Rugby library a fair amount just to, well, use it as a library, but his time there was disrupted by the band. I'm not convinced that it worked overly well in persuading people just there to see the band, to use the library as a library either.
I like libraries, I like gigs... but I don't go to a gig for the library, nor do I use the library expecting a gig.