same here - I learned the hard way about buying lesser or used mtb components, ended up replacing just about everything, an expensive way to build up a bike. Don't know what I spent on the mtb, don't really want to know...
When I built up a road bike, I didn't make that mistake twice. Got a nice carbon frameset, and a brand new Campy Chorus group. Ended up spending around $2200, but it's exactly what I wanted, and has not caused me the slightest problem in the last year of riding.
You can always put some slicks on your mtb, and pump up or lock the shock(s). I started back into road riding like that, it actually works pretty good. Until someone loans you a real road bike, and you hit a fast downhill...