+1 on a cyclocross bike if you want a new bike. I've had that on my radar for months now, as there are some commuting routes I'd like to alternate into my routine that have segments with crushed rocks, gravel, etc. I already have a road bike, MTB and hybrid. The MTB or hybrid could handle the off road portion ok but then they wouldn't do as well on the road section, and I much prefer drop bars in general. If the bike is "too fast" for rides with the wife, then just ride it slower. Or put it in a too-low gear and spin more. Or put a weight on it.
A friend of mine recently got his first decent bike and I convinced him to get a cross bike, and he loves it. I got to ride it a bit too.
29ers are MTBs. You could get a hardtail and put on thinner less aggressive tires and lockout the front shocks (if they can be locked out) but it won't have the advantages of less weight and drop bars that a cyclocross would and in any case it sounds like your Specialized already has your MTB needs covered.
Last edited by idc; 01-03-12 at 07:45 AM.