Z4M you can still find some with miles for not stupid prices, but it does feel like that market is starting to move away from rational now as well.
Could consider an older Cayman S? Doable for well cheaper than a lot of what we're talking here. Some engine risks of course, but your entry point is low, aftermarket support also massive. And in competent hands they can shift too.
Hard to know your exact use case, do you need 4 seats? Do you have kids? Selling the Honda isn't going to net a lot of money in, but selling the 335 will get you a fair chunk towards a(nother?) fun car. So I'd probably keep the honda and just get another car. If you can live with a 2door/2seat, a cayman is hardto beat. An old car now, but I think the S still had over 200kw, so still very lively and as I said. Lots of aftermarket support. Probably around 400-500k gets you a very decent one. Whereas an F80 you'll be closer to double that for a half decent one.
Other left field options:
S2000
MX5 of pretty much any generation
Supra (mk5)
Z4 m40i (same car as above)
I really don't see the point in an E63/CLK55 or any of that ilk. Handle like dogs relative to the equivalent BMWs, on a pass a C63 is as near as makes no difference undriveable.
Really?
My C63 was fucking planted on the twisties, arriving at corners 20km/h faster than a M3 doesn't mean it can't handle or undriveable, it means you need to adapt your mind to a faster car. Problem is finding a C63 with a LSD and the big brakes.
Anyway are Z4M's really getting that expensive? Fuck do i need to adjust my insurance values then?