I'm not so sure.
2 30 backs have sold for stupid money on eBay, several haven't. They haven't always been high, though that term is relative. 2008 a loads went for sale on eBay for considerably less. Two went for a lot...White bespin guard was nearly 1k, but that's easily one of the rarest of the 20 ESB characters, and HST for around £800 as a lot of HST focus collectors were waiting for one to show up as well as the usual palitoy mob.
Bossk, Han Hoth, HRS, Lando, all sold for around the usual amount, below £500
A few years before, a load turned up on Vectis and they commanded the usual prices for things. And earlier this year/end of last year a load of 45a and b turned up on Vectis and sold for reasonable amounts.
Plus there have been a lot of behind the scenes deals that no one has seen where prices have remianed fairly constant.
I honestly believe there is a sudden surge in interest and that's pushing the prices up. Plus a number of people are buying things without any idea of the availability, believe anything with Palitoy on it is mega rare. That is pushing up the price an additional amount.
Palitoy figures are way more common than they were 10 years ago.