Hello FF...just for the other side of the coin..I had SPD, not as severe as some on here but was grim (as you know).
I discussed with my MW in labour room about it and the need to avoid having legs v. wide apart as apparently it is this that can lead to longer term probs. However DS went into distress and the docs when examing me didnt really take any notice of this.
I ended up with an emergency CS and have to say that even with the CS pain I felt so much better even the next day...went from being barely able to walk because of SPD to it being much more comfortable even with scar. I think having the SPD pain made the CS scar seem like no trouble at all.
I would say from everything i read pre-birth that if you are able to get a water birth then that would be an excellent option...apart from the support of the water itself you are less likely to be examined as often if you are sat in a pool.
If you do have a natural birth then i think the main thing is to avoid legs being in stirrups or midwives holding legs apart but i think this is easier said than done when time comes as its not exactly uppermost in your mind during a contraction!!
Maybe you could discuss with your midwife and say that if it looked like you may end up needing instruments (where stirrups used), then could you just have a CS in that eventuality instead?
Overall i would say that obviously a natural birth is the preferable option but if things seem to be heading towards a medically managed natural birth then maybe a CS would be better than that. If you do end up having a CS then I think the pain of SPD stands you in good stead for dealing with your recovery.