I also suggest that this lightweight version not only applies to hwcodec targets, but to all the targets; why? Well, I feel that for this year and a half that I've been using Rockbox, my player has been constantly loosing buffer ("free") RAM: in May 2009, it was something around 28.7MB, now (build not older than a week) and with the same features enabled (dircache, database), I get 27.3MB or 27.2MB for audio buffer.
According to the chart, during that time RAM usage increased by a few hundred KB, so I suspect a lot of that may be due to things like larger dircache or database, or just enabling dircache at all (it used to be off by default).
The chart only shows RAM that's used initially. Allocations during startup use additional RAM, and there are far more allocations than just the dircache.
My 5G iPod currently runs r30834 and has a 27.5 MB buffer. I feel okay with that. If there was a stripped down branch, I expect I'd continue running the trunk on the iPod.
(However, I do wonder what's using that memory. In rockbox-info.txt, RAM usage is 1272304. The buffer allocations, assuming the numbers need to be multiplied by 4, take up another meg. The PCM buffer plus plugin buffer take one more meg. If starting with 32MB, that would leave 28.8 MB.)