I think values of old Rover's could stand to be a bit higher, considering what good cars and how usable they are. However, there's a lot of other stuff available for £25k. You could get a Jag MK2 for that, a Rover P5b coupe, a Citroen DS, plus loads of classic sports car options.
Good examples of 4cyl cars should be around £10k in my opinion, particularly early cars as there don't seem to be many left. Unfortunately, they're still at the stage where many fixable cars get broken for spares or scrapped as the market doesn't seem to snap them up when they're available.