Yup, that would be my solution: I just wouldn't use that reverb. As a general rule, I tend to not use any instruments' built-in reverbs anyway, for the sake of CPU efficiency if nothing else.

I removed and reinstalled everything Acoustica 32 & 64 bit and found both MC8's Pianissimo "Cathedral" reverbs were still bad.
 
Pianissimo standalone only comes in 32 bit but also installs a 32 bit dll. Both have good "Cathedral" reverb.
 
The Mixcraft installed dll's are dated 2012.
 
The standalone installed exe & dll are dated 2009.
 
So I got rid of the 2012 dll's and replaced them with the 2009 dll. Tho only 32 bit it seems to work fine in 64 bit DAWs.

From what I can tell, the 64 bit DLL was introduced when MC went 64 bit. When this happened I suspect they also manipulated the 32 bit DLL.