Multi-out VSTi eat more CPU/RAM?

Does it take more CPU/RAM for multi-out VSTI, even if the additional outputs are not used?

I suspect the answer is yes, since the plugin is sitting there with eight outputs ready to go whether or not you're making use of them. Probably depends on the VST though.

For most VSTi plugs the difference is very small as most CPU-use is linked to playing notes. I did a very extensive test a few years ago (for an online article) with several plugins that where available as multi and single version. Even then with much slower CPU then today's standards the difference was to small to be bothered about. Even when you have a multi-instrument and load it several times to use them as a single instance the difference in load is very small. There are some plugins however that have things like free-running oscillators and those use CPU even when there are no voices playing. So with those it is a different game. The Mercury-1 from TC-Works was notorious for this. I think with modern plugins this is becoming a thing from the past... as are multi-timbral plugins tmo.