I agree with you in general Ian. There are still some good cheap 2nd hand bikes around, cb500's, er5's and the like, but nowhere near as many as there used to be. The almost endless supplies of decent used 250's which were available for pips in the 80's and 90's have long since dried up, and though I do like 125's, they are not really attractive to most people. The 'classic' scene also has a lot to answer for.
As you know, I like my MZ's and rode them pretty much exclusively for 20 or so years. However, I'll be damned if I'm going to pay £2000 for a 30 year old MZ 250. For goodness sake, you can get a really nice er6 or something similar for that money. MZ's we're always just cheap, reliable, characterful hacks to me, and indeed to all members of the MZRC back in the day. The crack was to buy the cheapest old nail of an MZ you could find, smother it in Hamerrite to keep the rust at bay, and then proceed to knock up stupidly prodigious mileages. Though it is still a worthy club, all of this has now largely vanished from the MZRC. It's almost the same for Jawa's, except that if you are patient you can land on a 2nd hand modern one for silly money. I paid £1800 for my 3000 mile 3 year old 350 classic last year. Unbelievably, this is less than I've seen old 634 oilmasters advertised for! You quite often see these being advertised at around £2000, and probably in need of an engine rebuild and other serious expenditure before getting a reliable machine. The world has gone mad!