ironically enough if you let people use old jumps the quality of jumps would probably go up, also if you put demo and soldier into one category you automatically eliminate the need for 3 bad jumps getting prizepool money... 
If old jump is a 10/10 then you'd still need a really good NEW jump to top that, they would end up showcasing all the good jumps, just that the rank placing would be different (it'd also probably be cool to include other jumps, perhaps not in the main video but something like an unedited unlisted vid in the description?).
As for combining demo+soldier to avoid not having enough good jumps is more of an issue with trickjumping being dead, I also dont see how you would be able to compare soldier jumps to demo jumps, its like comparing surfing to bhopping. But even if you were to do that the judging was so biased/poor over the years that I really dont think anyone would be able to rate them properly.