So I've had bad luck with the current driver, even though it was mounted against the thick concrete ceiling (so a little bit of cooling :p)
Currently, I have 3 LED bulb's connected to 2 drivers, so going from 36V to 72V is certainly an option, just a little bit of rewiring needed (connect the last bulb in series to the other 3).
The only reason I'm thinking of going for 2x 36 is that no rewiring is needed, and IF one of them fails, I'll still have 50% of the light in the bathroom

P.S. indeed, if we're talking about DIM+ DIM- on the PWM 0-10V input, we're talking about separate dimming control inputs, and I do have my answer now, which I stupidly could have gained from the datasheet

I can connect multiple modules to a single PWM dimmer.
I'm not sure what you mean with 'dimming capabilities I want'. I want to dim the LED's, would a 36V dimmer do it differently from a 72V dimmer? (I did notice that the lower wattage dimmer didn't have 0-10V PWm dimming input, so I may end up having to go with the 72V anyway)