It's a shame you never found out about the animal/chaos drive reuse trick, Mystic. Though it slightly seems like cheating, the only difference is that you don't have to go through the menu screen and playing the same level from different drives/animals. It doesn't make actually raising their stats easier, just not as tedious. In fact, that trick was in every version of SA1 and SA2, so maybe the devs put it in on purpose...
Anyway, the Chao Garden is what pretty much what kept me playing SA2 even after getting all 180 emblems. Much of it was me just trying to make many different evolutions of chao, and just plain watching it slowly change as you raised it. SA2B made things even more interesting with different color chao you could hatch, and breeding different color chao to make two-tone chao and transparent chao made things even more fun. However, there wasn't really much you could do with them(besides race it with a friend who also has a decent chao) after finishing all the race besides just raise them for fun.
As much as I enjoyed the Chao Garden, I think its better that the devs would concentrate on the actual game more. Perhaps maybe there will be a game based solely off Chao someday, and maybe even give it an RPG-like element to it(would be like a cross between Chao Raising and PSO, having races, fights, ect).