I say hold your cards (cars) until you know what's what.
I think this is my recommendation too.
Sell the L322, it's bland and can easily be replaced.
You've modded the 110 to make it more comfy, the 90 is 'hers' and the beemer ain't worth anything other than to you as a reliable car, simply 'cos no-one wants them any more!
I agree - If one of them HAS to go, then the L322 - largely because its the most complex and the most expensive to fix, and probably the one that will least like being unused for any period - I've a few mates with beemers, and a good one seems to stay a good one without too much hassle.
BUT, what do I know!?!? my disco did 4500 miles between MOT's this last time, the wifes Pug about 6000, so ??? We're not really "car" people.....
Best of luck.