I agree with you about the valuations. I follow the big auctions in USA, and I was a former collector. I've owned a 1991 Lotus Esprit Jim Clark edition since new.
Problem in the USA, and probably same for Europe, as I see it:
1. The big money guys, who are "lifting" the Ferrari, Aston Martin, Mercedes, and etc. market, do not know the Lotus. Not at all. And their purchases are about ego and bragging rights, not driving the cars. Consequently, at this time, there are no "big credentials" for having any generation Lotus in their garage. Peer status is not boosted.
2. The recent ramp-up in values for extremely mediocre cars is insane, spurred I believe, by "2nd tier" money guys who missed the earlier action and, therefore, are now priced out of the rare Ferrari, A-M, and Mercedes market. These people, following badge/insignia only, are driving up values of 2nd tier cars. How else can you explain the rocketing values of a MB 190SL, or a Ferrari Dino, which now fetches $200K in #3 condition? A Dino is a rebadged Fiat, from any way you want to look at it. Four years ago, one could not give them away.
3. Many of the writers about USA auctions are owners of classic Ferrari, MB, and Porsche. So it is gratifying, and self-serving, to keep the marketplace pumped up by their auction reviews. And there are writers with Fiat, Morgan, Triumph, Volvo collections/history, for example, but I have yet to read any auction coverage by any Lotus collector. So, there is little public voice for the marquee. Unfortunately.
4. So, as I see it, the big issue about Lotus: lack of wide-spread brand identity and respect. If the collector can't "buy" the envy of other collectors by having a Lotus in his garage, then the auction appeal is not there.
I wish it were not so. The biggest problem in collecting a Lotus is not mechanical, in my opinion, but the narrow market when attempting to sell it. Selling to another aficionado can be very straightforward; selling to an "outsider", though, can be brutal.
Nonetheless, I love my 1991 Esprit. One day, It will go to one of my sons, who probably won't drive it because their is no dual-cluch transmission or self-parking. Who, under 25 years of age these days, wants to change gears or learn now to parallel park? Just joking to all you under-25 gear heads.
Just my "two cents". Thanks.