I can't imagine any of the B&Ms going anywhere until they have to. They're certainly not easy to relocate given their locations and settings. If they're difficult to relocate, their value is lessened. If you can't sell them on as coasters, they're worth very little - so why get rid? It doesn't make any sense.
As coaster enthusiasts, I think our 'love' for particular rides dwindles quicker than it does with the general public. Don't forget, every single year a new generation discovers these rides for the first time and feels the 'magic', thrills etc that we have probably all forgotten about a decade ago.
Don't forget, people are still discovering the Pleasure Beach woodies for the first time!
That said, Rita & Spinball could be moved without too much hassle, I'm sure.