Personally, I don't think it the weight of the frame that aids in function, but the weight (or better yet, the mass) of the slide. That is why full-size polymer guns like a Glock run great even though the frames weigh next to nothing.
However, I am not a firearms designer so I know little of what I speak.
IMHO, a stainless frame on the R-9 (it always comes back to this, doesn't it?) would make the gun potentially more durable and potentially last for a much higher round count and would lessen the perceived recoil (not the actual recoil, but that is a different story).
However, lessening the percieved recoil and adding that degree of durability were not the design parameters as I understand them -- it was to build the smallest, lightest 9mm and make it suitable for pocket carry.
Incidentally, I took my R-9 Elite out to the range this weekend and pumped 100 completely trouble free rounds through it in about 45 minutes. I wouldn't normally do that, but I was testing K-Man's new wood grips.