The fact is that if you break it down into categories, you're losing the entire concept of "Mazda Forums' Ride of the Month" .. See, the thing is, the car that wins is supposed to be the 'favorite' car of the ENTIRE forums. That means ALL makes and models of Mazdas. It also means ALL types -- from the modded for show, go, a combination, whatever.
If we break stuff down into categories, does that mean only people with a Mazda3 can vote on the Mazda3's, and so on? How would we ever 'restrict' the polls to people with only a certain type of car? It will inevitably turn into a mess. Think about how many people and how much organization is put into actual car shows -- a LOT. There simply isn't the staff here to support such a thing.
While the idea is definitely unique, it's just doesn't strike me as feasible -- not to mention that it doesn't even fit into the concept of what this whole contest was created for in the first place.
.. If any of that actually makes sense to anyone other than me, LOL.