Wholeheartedly agree that it would be best to get your OH to try the wools of other breeds and find out what she likes best.
The longwools are the most labour-intensive breeds to keep, I'd think. We are just considering getting some Teeswaters ourselves, and will do more research on exactly what it would entail before jumping in. Certainly lots of dagging. flystrike would be a real risk if you were in the sort of place where you get a lot of flies, BH thinks I'll need to keep them washed, as well as dagged, and I expect to have to clip twice a year to keep them comfortable.
Spinning-wise, longwools are a different kettle of fish altogether. Too long for carding, you had better like combing! And even when starting with commercial tops, it takes a bit of doing initially to do the low-twist worsted spin required. (I'm getting there....)
I agree with Fleecewife, the easiest fleeces spinning-wise are those in the mid-range of staple length. A nice Shetland you can comb, card, or spin from the lock, however the mood takes you. It'll felt too, if you fancy a bit of felting.
If you want to be helping a rare breed, you could consider a down breed (Oxford or Dorset Down), or the Hill Radnor or Dorset Horn - or the delightful little Portland, which would be more like your Castlemilks in looks and temperament, but have a more readily spinnable fleece. Some Portlands have superb fleeces for spinning, some a bit more ordinary - but you could select your foundation stock on the basis of fleece quality, and breed to improve.
Do keep us posted on what you decide and how you get on!