Just got home from viewing 2, I think it's actually better the second time around. Some things I noticed:
1) The two "too long" scenes that specifically get brought up, the intro/battle with Groot dancing, and the Rocket/Yondu escape, on second viewing, and keeping in mind comments, feel like the action is there to provide showcase to the song, hence why the scenes go the full length of the songs.
2) Mantis' use of the word "progeny" that Ego was searching for. Child/children would be obvious plural or singular, but progeny can be either.
3) Ego's "look of pride" when Peter was able to manifest his powers is much more sinister when you know what's going on.
4) There was a scene, I think fairly early (pre-Ego's planet, IIRC), where there was some dialogue that seems like it's a reference/shout-out/Easter Egg to something. I caught it the first time, and it stood out to me, but I dismissed it. I caught it the second time, and it stood out again, and then I remembered that both GotG and whatever the reference was to are both owned by Disney. I just can't remember what it was or who the conversation was about! I want to say it was Peter, and possibly Drax or Rocket. And they were on a ship at the time.
Oh, and as for the question about ID'ing songs/singers... From Amazon's listing for the Vol. 2 Cassette:
So, yup, case has the listing.