I have a friend that's got some low-end Alu frame, hooked up with some '04 LX parts.
He uses his bike for both off-road and road trips. He's got two tire sets, some Continetals 2.1 for off-road, and some Ritchey Slicks for the road (1.9 or 1.75, can't remember for sure).

In my opinion it's the best solution