Old music, new music - you can't define the value of that music except to comment on how long it has been popular or how many people it has affected.
Much of this nu-metal / rap etc will not stick around long enough to have the kind of influence or affect that the beatles had. Personally, I think the new GnR stinks, but that's just MHO.
I also agree that unless your solo has a point, don't put it in the song. You'll just look like a wanker.
-Daniel