I probably haven't seen Love play enough the last 2-3 years to really appreciate how good he is now. I think I have a pretty good idea, but it's still tough to gauge exactly how good he'd be on a better team. I feel like his scoring might be a little inflated right now from playing on a team without much else for scorers, and yes his defense is obviously not great. That is the main beef with Lee as well, so they're a wash on D probably, but losing Klay's defense in the process would hurt.
Klay at this point I think has a pretty good reputation on D and it's well deserved. He's a good defender and his ability to guard point guards and stay in front of them makes him a great fit next to Curry on that end as well. In the West where you might have to face Westbrook, Paul, Parker, or Lillard in any given playoff series, it's huge. That's why offensively and defensively, they are just really balking on trading Klay. Bottom line is he will likely be a 20+ ppg scorer the next few years who fits well next to Curry on the defensive end. I think by their thinking if they're going to trade him for Love, Wolves should feel they are lucky they are getting that much since Love is gone either way.
Yes, a lot of people value Green more highly than Barnes. Green showed he can really play especially towards the end of the season and into the playoffs. Played some pretty good D against Griffin in the playoffs and I actually would prefer to see him start next season over Lee if we don't get Love. He was contributing more consistently than Barnes last season, however I don't value Green more highly than Barnes myself. Just as Green really improved a lot last season, I expect Barnes to do the same this season. In their rookie years, Green largely looked like shit btw while Barnes showed many more flashes of being a player.
Generally though I get that Love is a great player, and yeah that pick and pop would be fun. I really wanted them to find a way to get him coming out of college cause he was exactly what they needed at that point, but that was before he blew up his shooting the way he has. I appreciate that he can box out with anybody on the planet (sometimes I think David Lee doesn't know what a box out is). I'm trying to quantify what it'd mean to have Curry and Love together. Closest thing I can come up with is the Nash - Nowitzki combo early in their careers.
Seriously though, what do you think Love's upside is, offensively? Can he be Dirk with better rebounding? I know Dirk is longer and in his title run that made all the difference because he was making shots that were simply unguardable. Not sure Love will ever be able to hit those big time shots that really set Nowitzki apart, but you've seen him play a lot more than I have.