If it doesn't support AGA modes, would it best be used on a non-AGA machine like the 3000 or 2000 (I know the question sounds really silly)? I have a CV64/3D in my A3000, and I might transfer that to my 4000, and get an MNT for my 3000, instead, and use the CV for AGA/24 bit modes on the 4000. Would this work?
If you really need the 24-bit pass-through then that's certainly a viable scenario. Personally, I can pass on the native AGA for the benefit of HDMI, increased video memory, and massive screen resolution offered by the VA2000.
In fact, I currently have two 4000Ds. One which I have been using as a test-build machine and has the VA2000, the other is my daily-use Amiga and has a Picasso IV. Right now I am considering a PPC purchase for my main 4000D and if I go that route I will swap video cards and dispense of the venerable old PIV. (Not without some reservation or emotion as the PIV has served me well for the past 10 years and made my Amiga experience all the better.)
There is very little I do in a native Amiga screen which requires 24-bit. Even some of the AGA WHDLoad games I think I will get away with just fine.
Or, I could save the PIV and sell the Spectrum 28/24 in the extra 4000D, and put the PIV in my 68060-based 2000. So many options, and ultimately a matter of personal preferences