rebuild is an automatic way to : open, edit, save EVERY post
but for 50 posts, is it worth it? that has to be your call.
if you do it, i'd suggest a pre-backup, then fire it off, watch Monday nite football.. come back..
note: you can always kill it in the middle, if you see it taking too much longer than anticipated too..
bummer is, that it starts the rebuild from lower post numbers ( older ) and finishes with the higher ones ( most recent ), so you really won't be doing anything of value until the last maybe 5% of your posts, where those blanks exist.
you'll have to decide for yourself.