A lot of the small coffee places in town are very similar in quality I've found, I'd welcome Starbucks to Galway. Places like Starbucks are what tourists expect from a city nowadays, I don't think any tourist has gone "Right, I'm not going to any city with a Starbucks". I don't see why Galway can't have the best of both worlds and have popular European chains like H&M and Starbucks and still keep it's originality, if Starbucks is as bad as is claimed then the smaller shops won't notice any drop in sales then.
It brings jobs, and a place to relax in town (that isn't a pub) and isn't that overpriced in it's food compared to some outlets in town (two buns and coffees in Arabica cost me an arm and a leg the last time).
Personally, location wise? Bar 903's old location or the spare unit beside HMV would be great for it.