In general I would clearly try to be distinctive from the competition, don't be evrything for everyone.
If you read yellow pages, there are businesses that have such a fluffy proposition, I mean just read all the ads in the section for cleaning companies, there will be very few that stand out.
I actually like the SG idea, even the AC/DC idea would be good, sell everything that AC/DC play or that makes an AC/DC sound. The right SGs, Gretsch, Marshalls, TubeScreamers, BoR, etc. Obviously you'd need the best collection of AC/DC T-Shirts, DVDs etc as well.
That would be really distinctive but at the same time attractive to a big enough audience. Who knows if you do it smart, maybe Angus will drop by one day 8)