I tend to do nearly the opposite. My beaters become more and more beat up. Eventually, something gets so worn out that I replace the bike rather than just parts that have broken... and i replace it with another beater. Oh, and when parts break, I don't upgrade, I just replace with either whatever's lying around, or with something cheap from Nashbar.

I got rid of all my non-working bikes (I still have a large collection of usable parts though) so I only have two bikes. Both are definitely beaters.