Actually, Tsukuba has even more bumps than the GT4 version, it's the nurburgring version that is lacking some important bumps compared to the GT4 version, PD went all out in getting that track right, and judging from the videos (of real life time attacks) i've seen, the GT4 version is defenetly the best of the two in nurburgring, but the Tsukuba version is missing some minor bumps, but it's pretty much the same.
as far as the other tracks go, dragon range seems pretty uneven, i like it a lot, but i'm not a huge fan of the other closed circuits, the rally ones aren't fun at all, they should've made the rally ones like they did dragon range. (a "stage" instead of a closed course)
I wouldn't miss any of the rally tracks in either enthusia or GT4 (at least the gravel ones in GT4, i hate them, the tarmac ones are fine.)
Richard Burns Rally is the only sim that has proper rally stages, and they are awsome, specially because you can go off the track to gain more traction on some corners, just like the real life rally drivers do it, oh and they have tons of different ground types, some grippier than others.
So yeah, i think GT4 and Enthusia could do with out the "rally" tracks.