Thanks to everyone for chiming in. All of the perspectives are helpful.
I'm with a large practice, so I see a number of different doctors, so with each visit, I keep "polling" them about their opinions on the matter. One of the docs I respect the most said, "Its too early to worry about it... lets wait and see how things go. Your first babies were both big (8.5 and 8.11), so its definitely something to consider if you get to 36 weeks and your baby is measuring big again... but... if he/she is measuring smaller (6 lbs or so), ... we should just wait and see." That certainly makes sense to me, although honestly I cannot fathom having a 6 lb baby unless there were something "unhealthy" about my pregnancy. (I know there are lots of perfectly healthy 6 lb babies out there... it just seems that based on past experience, my body tends to create big babies -- even though neither I nor my husband are very big).
I think one of the things I need to get more info on is the relative risks for planned C-sections of healthy moms/babies v. risks for all C-sections. As much as the broken tail bone SUCKS... as one poster pointed out, no baby has ever been hurt from one, and no mother has ever died from one,.. and I have 2 (existing) kids I need to think about. So even though the risks are relatively small, I wonder if its selfish of me to take even that small risk instead of suffering through the tailbone recovery.
but boy... it would be nice to feel better a couple of days after delivery. As you all know, new moms get up and down about 200 times a day... and getting up and down with a broken tailbone is so bloody painful.
Please keep any thoughts/opinions coming...