I'm stuck on Vault 3 in the lower, possibly lowest level. If I try and use the doors to go back to the recreation area, the game crashes. Have tried saving, clearing my cache and the one thing I won't try is reverting to an older save and losing loads of progress, because that's like me telling Oblivion to revert to a newer build of the game - one that isn't bugged to f*ckery.

Well you can either wait for a patch, but that may not fix the problem, but your best bet is to unfortunately start again.