I hear what you're saying, but I've never really had a problem. BUT, I do use a lot of forums using the more recent vBulletin format of user details above their post content, this means I'm used to skimming over the top block straight onto the content.
I'll try a few things to see if I can make the post area more clear, but I don't really want to darken the grey up if I can avoid it (not least due to the work in changing the avatar background colours

).
Some people maybe don't even know there's a grey, to those folks, you need to adjust your monitors, if everything is white, your brightness is too high, your contrast too low, or both.