BaT has listed 77 E9s since December of 2015. Excluding the one Batmobile, here is what they sold for (or bid to if they didn't sell)...
0-10k 2
11-20k 5
21-30k 14
31-40k 19
41-50k 6
51-60k 6
61-70k 6
71-80k 9
81-90k 3
91-100k 0
>100k 6
I think BaT has become a good (maybe the best) marker for collector car values. Especially for those make/models that they have put 50+ at auction. It becomes relatively easy to find several cars that ran on BaT close to the condition of the one you own or the one you are looking at to purchase and determine how the market values it.
I usually don't put much stock in Hagerty valuations. I can't find how they determine their values but I suspect they either come from insured values...and most of us over insure due to the low cost of doing so...or big name auction houses catering to high end cars and deep pocket buyers where the seller nets far less than the "selling price" due to entrance fees, commissions, transport costs, etc.
43% of the BaT E9 offerings sold for or bid to between $21-40k. The median is in the high 30's. The two cars that ran recently on BaT were bid very close to how E9s in similar condition have been running on BaT. In any case (IMO), the market has spoken.