Dingbatt: I believe the reason it is a dome is twofold. Firstly to make it feel less claustrophobic and secondly (and more inportantly) so the condensation runs to the sides rather than forming cold drips to fall on you.
Didn't think about that ...
Our main bathroom shower is a cubicle that is completely enclosed. Yes it does get steamy and a little sauna-like, but the bathroom doesn't have an extractor fan (house is about 40 years old) and having the shower fully enclosed, and training the kids to keep the doors closed during and after showering, makes a huge difference the the amount of condensation in the rest of the bathroom (and in the house as a whole).
It's amazing the amount of condensation visible in our (small) house when you shower with the bathroom door open ...
The growth of mould may be promoted in the cubicle itself but regular cleaning keeps on top of that, and it's better than having to de-mould the whole bathroom.
.... or de-mould the whole house...