Been on bicycles since I was 3 and motorcycles since 7, I find that I am better at both when practicing concurrently. Downhill has become one of my favorite pastimes in the Summer (living in CO stuff like that is mandatory), and although it is not the same as motocross which I gave up long ago it triggers a lot of the same skills. I also have a couple of really nice little bike parks not too far from home where I can get out on my 4x/slalom (like a bmx but 26" wheels and a bit of suspension) and enjoy dirt jumps or pump track.
Being on 2 wheels is awesome no matter how you do it.