Amateur perspective here...
I can't sing, but I love the sound of the human voice better than any instrument. I can't act, but my research speciality, before real life got hold of me and forced me into aviation safety, was a kind of medieval Japanese comedy, which is mainly mime, jokes, and a few little tiddly-pom type of songs here and there.
So, if there's dramatic interest in opera, my eyes are open to it. However, for me it's first and foremost about the music. Absolutely, and forever.
It's very nice if the singers can act a bit, but they can't very well go tearing up the furniture and swinging from the flies, unless they're lip-synching. So yes, an opera singer's acting is likely to be mostly expressive movement rather than something that develops the plot or character all by itself.
Just think about those opera sets. All those huge backdrops and gorgeous chunks of stage furniture, and these days lighting too...isn't it a kind of compensation for the fact that the main characters *won't* be moving round and attracting your eye very much?
Now that it's possible to reproduce moving pictures and sound at reasonable resolutions, I think we'll be seeing a lot more musical or operatic work on DVD or whatever new media come along. Don't hold me to it, but opera or musical drama of any kind may turn out not be a career backwater, if that's what you're frightened of.
As for the techniques of acting, people learn that stuff to a certain extent, y'know.