I think Brompton have been milking a now very overpriced product for too long with only minimal development. Cyclescheme has enabled them to push an M3L from £500 to £1000 in ten years.
You keep saying this but it seems your memory is not correct. Looking at the price lists a M3L did cost
£391,28 in 1997
£735 in 2010 (for a key model, £765 in B-spoke version with choice of colors, with the carrier block being another £15 on both ) and
£1060 today (according to Brompton's webpage, including free color choice and combination apart from premium colors and including the carrier block)
So while there is a very recognizable rise in price it is clearly nowhere near of what you claim. Regarding the development of the bike: If I had the choice I would clearly prefer a 2020 model over a 2010 one, even at a higher price, as components have been enhanced massively. And I would not even think about a 1997 one. The interesting bit is that used 1997 models are sold in the range of what they costed new and sometimes even above that. I bet there are not too many consumer good where this is the case (don't even imagine to compare it to cars....).
If you look at how other prices have developed over the last 10 years I'd assume Brompton's rise is not massively above that if at all. I'd hope for you that you got a pay raise as well during the last ten years...
So in reality not too much to complain about I'd assume.
Probably need to prettify the brazing a bit (or pick the nicer ones off the production line) since it shows. You know the lacquered frames rust under the lacquer? Some people like the steampunk look that results.
One more of the statements that seem to be based on a 15 year old state of things. Raw Laquer was introduced in 2005 and stopped in around 2008 due to the problem of underrusting (which still was only a cosmetical problem, still a pity if you pay more for the looks that then turn worse quickly...). Raw came back around 2010/2011 and while the rust issue has not been totally absent since then it has been not much of an issue. With more recent bikes I do not know a single case (while my 2015 raw model has a tiny spot which did not change in years) and as there is now additionally black laquer as well as flame laquer I'd assume the issue is long gone in the meantime.