The safe boot is just general OS X maintenance, so a safe boot could only help java memory problems indirectly, if at all.

Cleaning out the incomplete folder is also good practice (incompletes that try to resume use up memory), so that's another way to reduce memory demands.

I find concentrating on just two or three downloads at a time helps, and hiding LW overnight also helps.

Wish there was a quick and easy solution, but I can't think of any others.