Re: mailed discs... I've been getting them for years from either blockbuster or netflix, and after seeing a disc sit unwatched for a month too many times, I made a rule. If it sits unwatched for a week, I just mail it back. If I didn't watch it by then, I must not have been that interested.
Re: collections... My collection mainly consists of all the dvd's I collected from the dvd era, ripped to hdd. I will buy a blu-ray if it's a movie I really love, but usually only if it's a really good deal. So while I do still collect, I do it less now that so much streaming is available, but I'm not quite to that point that I don't find it useful anymore. I do think that is the direction, and as pipes continue to increase in size and get cheaper, I think eventually the strong advantage blu-rays have now will diminish or disappear completely, so to answer the OP - not yet, but probably soon.
Re: rewatching... many favorite movies from my youth, up to about 25 years old, I rewatch fairly often, and I love concerts or music related movies/documentaries, and find they have a ton of rewatchability. But newer movies, unless they really strike a chord, I will never watch again.