I run different wheels on my MTB too, changing wheels isn't an issue, providing you have the wheels to change of course, that wasn't my point?
I would argue with anyone that good quality rim brakes are equally as good as discs in the dry for 95% of riding. The discs come into their own on Alpine descents, but not to many of those around Worcestershire to be honest. And of course in the wet, when yes I agree discs are better of course they are. BUT...its a bit like driving on the ice in your car, you make allowances for it. I also accept that from time to time something will happen that we require a sudden stop and with rim brakes you may have to look a least than ideal way out, usually via a hedge!
On the flip side, if you have to brake that hard with discs, either you're going over the handle bars or your tyre looses traction, either way the end result will still be same!!