If you can get to 300 resources, it won't be much longer before you can get to 400. To me, either is virtually identical, as accumulating that many resources pretty much means that you have a lock on the game already.
Because both seem the same to me, I have no objection to changing to 300. I agree with Progressor that it's not needed, but I also think it will have little effect. Those who win via resource victory will still do so under the change; those who don't, still won't win in that manner. You really can't win that way on accident regardless.