Following the change of ownership in MMC there seemed to be a concerted effort to increase the market price of used Aero 8 cars - which I understand as a strategy as it helped with the positioning of the plus 6.
I would agree with Peter though, that this strategy has probably peaked with the £280k Aero GT, the £225k Aeromax and the £189k Coupe looking a bit topish to me. You can buy a huge amount of very capable/ desirable car(s) for that sort of money.
The recently advertised Supersport for £139k and the 2018 50th Anniversary plus 8 at Sytners advertised at £89k seems like the market is moving back down a bit.