I can use ~10-15 unique foliage trees without serious problems, but then it becomes a problem - i think this limit wouldn't change if FP shuffles the randomID, but it would be a timesaver and is still better then use the FP transform params.
on the other side ..if shuffling the IDs isn't possible then there could be another timesaver:
FP can handle at the moment on my machine(quad, 4gb ram but on 32 bit system with max2008) ~40-50 trees based on one complex Foliagetree (can be onyx or xfrog too) without crashing ..which is fine, but if the custom object is converted to a vray/mr proxy the whole picture changes and there is much more possible...
It would be a timesaver if FP could convert such trees before it renders, because then the custom tree would still be editable, which a proxy isn't.
..just some thoughts...