I just had a few days ago, an out of memory error from galciv2 while quicksaving the game (4GB of ram + XP64) (sidenote: launching process explorer AFTER the crash showed me a peak memory usage of about 3GB with 1GB currently used by windows and other programs, so I think galciv2 just crossed the 2GB treshold)
while searching for other things for other games I stumbled on this information :
Apparently all you need to do is to set a simple "flag" or bit on the executable to allow it to access higher than 2GB addresses. And I of course already checked galciv2 executables and it is NOT set.
Q: Are there any other changes necessary to take advantage of 4GB virtual memory ?
A: No, only the LAA bit needs to be set with either a linker or binary change. no other source code or binary changes are required.
Of course I have the knowledge required to do this myself from my poor chair, but this is against the laws as far as I know. So just suggesting stardock devs to look into this, if they ever want so as this is ... like a 10 seconds modification, ok 5 minutes if you take the time to carefully read the document I linked to.