Neither of these companies have any open jobs- you've already probably pushed too much. If they DO end up opening more they may remember you as "that guy that had a good resume but was super annoying so we don't want to work with him"
Strongly disagree. First of all, of course you want to be polite and respectful of their time. That said, many companies say they keep resumes on file for six or nine months or whatever. That's a lie. Unless you are a truly amazing candidate your resume goes straight in the garbage can after they look at it, and even then it still probably goes straight in the garbage can. Truly amazing candidates don't look for jobs long. So unless you are great they won't bother to try to look you up, and even then they probably won't, knowing you've likely moved on. If you are mediocre they'll definitely look for somebody better. So if they have a job down the road they'll just put out another job post and see who applies. The chances of them getting back to you in the future are approximately 0.0%. I say "approximately" because it could happen, but in reality don't plan on it.
There are two possible scenarios: 1) They don't have any open jobs, which case following up costs exactly nothing. What are they going to do? Not give you a job? They already are not giving you a job. Or 2) They
might have a job but aren't sure how to move forward, in which case following up demonstrates you are a person who follows up and by showing interest you are solving one of their problems. Look at it this way: As employer, do you want an employee who politely waits for things, or do you want that obsessive person who doesn't relent until the job is done? The latter, of course. You want to hire that obsessive freak who can't rest until they have explored every detail. And again, what are they going to do? Not give you a job? They already are not giving you a job. The reason why the old saying "the squeaky wheel gets the grease" is an old saying is because it is true. You want grease? You gotta squeak. Again, you want to be polite and respectful of their time. A quick email is fine. I sometimes include a line to the jist of "Just touching base, re: XYZ. No response necessary if things haven't changed." About 99% of the time people respond when I tell them they don't have to. Draw your own conclusions there.