A few is fine (four perhaps) but if you're going to do them then at least make them long enough. Mount Wario is the longest and that's arguably slightly too short as well, whereas Big Blue and Rainbow Road are woefully short (even if highly enjoyable) that pulling a Wario Coliseum and giving two laps of each would have been preferable.
The issue you have with making long tracks the norm is that they take longer to make and they lose a little bit of the magic and uniqueness of the "long track" in the process. You have to strike a fine balance, and MK8 was pretty close to that if you ask me.







