This bothered me, too; I hate having text crammed up against a block of solid color. It makes me claustrophobic.
Here’s what I did as a workaround (in MacVim, but I expect the same technique will work elsewhere):
In your preferred colorscheme, set the background color of the line-number column to be the same as the background color for normal text, and the line-number foreground color to something low-contrast and unobtrusive (so it doesn’t look like it’s part of your normal text). I use white-on-black for normal text, and dark-grey-on-black for the line numbers:
hi LineNr guifg=#505050 guibg=Black
hi Normal guifg=White guibg=Black
Admittedly, this doesn’t fix the problem so much as hide it, but it’s worked well for me.