While it isn't absolutely necessary (as when you're reading a good book), I think it does enhance, and I miss it when it isn't part of a VN - especially since I've gotten used to some Devs that do it so well (Drifty and Caribdis, for example).
But, for my taste, leave out the voice acting, with the possible exception of decent "moan" type sounds during sex scenes - subtle stuff, not that ahegao crap where the porn actress sounds like she's having an orgasm just because the guy is within three feet of her. I also like when a Dev will put in something like the "announcement" voice where it makes sense (e.g., Caribdis in Eternum when you're logging on), and things like indistinct background chatter, nature sounds (rain, waves, wind, birds), or even traffic noises where appropriate - things that help create the atmosphere of a scene, but which don't overpower.
My two cents; you're mileage may vary.