There's a whole lot to be said for 'do it once, do it right'. I really tried to do that with my car and even so, I'm -still- working though little bugaboos on it at least every month it seems. I don't think they're ever truly "done".
If you do go with a 12-bolt, keep a couple things in mind. If you go 'used', there are folks out there who will sell you a "Type O" rear-end out of an Oldsmobile and claim it's a 12 bolt because it has 12 bolts holding on the rear cover. They aren't. Inside they still only have 10 bolts on the ring gear and aren't any stronger. Sometimes they truly just don't know, sometimes they're being dishonest.
On a 12-bolt, I'd recommend making sure you use a c-clip eliminator kit, and make sure it's one that's approved/recommended for street use (not all of them are). If you ever DO go to the track, most sanctioning bodies require them (and besides, they're just safer).
That's one of the reasons I utimately decided to go with a 9" - that, plus the ability to change ratios by swapping pumpkins and they're stronger. (but they do have slightly more parasitic drag)