For me personally I have yet to read any high school/college AU’s, so I cannot have a real solid opinion on them. Having said that, from what I gather from others they’re fun to read and there are a couple of quite popular ones out there right now.
I struggled with reading AU’s at first because I am just so picky when it comes to reading fics that I needed everything to be absolutely in character and Loki not to be this fragile china doll that could break if breathed on. However, I’ve come to let go and realize that AU’s are exactly that, an AU, and the characters aren’t always exactly what they are in the films/comics. I treat AU’s as entirely different characters that just happen to have the same name, similar back story, characteristics, and nuances. Once I came to that realization and gave myself permission to start reading them, I am all for it and they opened me up to some wonderful writers (Kytt and Midnight Ophelia being two of them).
Sorry if I went off track there. :P
Short answer: AU school/coffee shop fics = good fun (or heartbreaking angst depending on the story).