I think the multi platform bonus is a good thing and it sort of caters to the community feel of the competition. (Encourages to release to a greater number of people within the homebrew sceen).
Most games will probably (wild guesswork here) not have a too complex control scheme, so I don't think the controls would be affected too greatly.
Even if it did, the small amount of bonus points awarded for the multiplatform thing wont (or rather should not) outweigh bad controls or any other problem that arises from "being stretched to thin".
I guess that a sort of solution to the unfairness problem could be that a multiplatform game would be judged individually on each platform it supports and then take the average of that score.
This if it plays awful on one platform, that would drag down it's score.
My reasoning builds on that the amount of points awarded for multiplatform support should be quiet small and only there at all to encourage devs who feel that they could include it to include it.
Either way, I will try to release something, hopefully for more than one platform.
But even if I had no intention to do so, I would still think a bonus for multiplatform support would be nice.
I'm not so sure about the older platform bonus tough, I can see the reason for a bonus for releasing to the gp32, in order to try and increase the flow of new software for what is,
more or less, the spiritual grandfather of most handhelds in our community.
But I am not so sure if it's enough of a reason.
I guess that it is probably harder to dev for the gp32, but this is wild guesswork at work again