I tried your suggestions with mixed results. The compability modes did nothing and neither did updating to the newest Nvidia-drivers.
The switch to the 32bit version of Attract Mode sort of remedied the problem though: Switching from game to game still hangs like previously for the first five games or so that I scroll through, but after that everything suddenly works like intended. While not ideal, this is FAR better than before and I will wait on further versions of Attract Mode in the hopes that they will somehow fix whatever the problem is.
Regarding clean installs: The install I mentioned that worked, was 1.5.3 and was transferred directly from my main-system, whereas the others have been installed directly on my arcade-PC.
Before trying out the 32bit version, I also tried to install several different versions of Attract Mode, and strangely the problem does not exist with V1.6.0 and everything before it, but started after that version.
As said though, the 32bit version takes care of most of the problems and is workable for now. I am still hoping that a newer version (maybe 2.0 Final) will somehow take care of it altogether.
Thanks for your help on this Omegaman - I appreciate your input.