it depends on what anime...but most of the time...yes adding computer effects does ruin it...I'm not sure if this is anime or not but I've seen this Code Lyoko show on CN and I hate it -_-
they've been doing it for years and I don't really see them stopping anytime soon, personally I think that if its well done it can make for a great bit of special effects, on the other hand I've seen it done so poorly that it takes away from the anime and you end up thinking gawd that was the worst anime ever, if only it had a bit of moviephone.com in it, then every thing will be better.
I haven't seen a show (or movie) yet where CG additions "ruined" the show/movie.
But sometimes it doesn't always look too well to do it, no. It should be done carefully, if it's going to be done at all.
I don't know it'll ruin the anime. I've seen alot of good anime with 3D. Some have 3D occasionally, others have like 80% 3D. And almost all the movie versions have some 3D more or less.
it depends if they use it alot i think its sad because then they are not very good at drawing anime, but then again making computer animation is like an art form. now i'm confusing myself. overall it depends if they use it in moderation and if it blends in.