This is really no different than the Marvel Cinematic Universe and we've maintained a relatively high level of quality with the worst films being just decent, which is going to get even bigger as time goes on. They're working out two or three movies every year for the foreseeable future culminating in Avengers 2.
I guess if we look at the "Trilogy" films as Avengers and all of the other standalone films as the Marvel solo movies, one per year doesn't really seem that excessive. And it's unlikely that the creative staff will be doing one movie per year, but different creative teams per film (writers, directors, actors, ect) with a few people overseeing the entire project/universe like the Marvel Cinematic Universe. I don't think one Star Wars film per year is really that bad when looking at it this way.
This is exactly how I look at it.
And the thing is, after the PT ended, I didn't expect any more Star Wars movies. Just the possible live-action series, which, the more I read about, the less good it seemed, not to mention the less likely it seemed. So these can only be a bonus, an unexpected treat. If they're crap - well, I don't have to see them. I'll still have the previous movies to watch. They can't be taken away.
There is limitless potential for SW movies, especially now that numerous writers and directors can be brought in to make them. Gangster adventures with Hutts and their acolytes. Jedi derring-do. The adventures of Han Solo or Lando Calrissian. Young Qui-Gon and his Master Count Dooku. Mandalorians. Boba Fett, anti hero. Etc etc. If even 50% of these are good, it's still a lot more than I'd hoped for when I walked out of the cinema at the end of ROTS.