Yes, I have a hard time getting back into revisions of a story sometimes, especially if I took time off the story to work on something else. When I started rewriting my novel, it definitely took a while for me to hit my groove, because I'd taken several months off it to let my beta-readers read and respond, and then for me to get back into it. (In retrospect, I think I took too long.) Usually, though, I'm able to get back there by reading through the story once or twice, getting back into the head of the narrator and/or characters.
As far as adding stuff, yes, people who have read it before do seem to notice, but that's because I left something out that they wanted closure or an answer to, or some gaping plot hole. (Usually, when I'm sending it out to betas who have read it before, I ask if this bit works for them now. Also, I might send it to someone who already liked the story to find out if I'd screwed it up somehow, or send it to someone who hasn't read it before.)
I think in short, I'm for two things: 1) shorter time gaps between revisions and 2) figuring out how to trust myself more.
That second one is going to take more work, I think.