Also, I'm not familiar with that particular bike, but if it was built with a more slack geometry, and you plan to just ride it on xc type trails, dropping the front and giving it a bit steeper of a head-tube angle might not really be a problem anyway. Do you know how many degrees the head tube angle is with the bike in stock form?

I'm guessing headtube angle is the handling issue the bike shop guy was talking about. Once you get past a certain point, the bike will become twitchy and more difficult to keep going straight down the trail.