Until AE gets reprogrammed to use 64-bit Operating Systems, and you’re running a 64-bit OS as well, AE can not use more than 2 GB of RAM. It’s a 32-bit OS thing, apparently.
It’s my understanding that AE only uses as much RAM as it has to, and using more RAM won’t speed up your workflow — it will only allow you longer RAM previews prevent renders from crashing, and probably avoid disk caching when you fill up your RAM(though I’ve never seen that).
If you can RAM preview all the frames you want, and your renders aren’t crashing for lack of RAM, then you have all the RAM you can use, in my opinion. Until AE gets 64-bit aware, that is. Have you found that AE won’t let you RAM preview your entire work area, but still shows that it is using 60% of your RAM?
Steve