Acura guy is crazy, stupid, jealous, or.. I don't know. None of those mods will hurt the car in any way, at all. I had a '92 GSR also (what color is yours?) and that stuff, all typical bolt-ons, are completely harmless. As for 15 hp...well, maybe if you're REALLY lucky, you'll get 15hp from all three of those mods (intake/header/exhaust), but it's unlikely.
As for "is it worth it"... I can't answer that without knowing how much they're asking for it.
None of them will make your 'idiot lights' come on, either. Will it make the car quick? Well...quicker than it is, I suppose. But I'd say go for it... DC is pretty reputable. What's up with your Acura mechanic? Hmmmm....