Yeah, and I would add that he's a great guy to have at practices and internal scrimmages. This is again something most people overlook since cameras don't show it; but the same way you have your lazy-ass Iverson's "We talkin' 'bout practice!" who don't give a about anything besides their on-court play, you also have your "100% energy all the time" guys like Keldon or Westbrook. And (again in the right context) I'd much, much rather have the latter on my team. It makes everyone adjust to their energy and have to play harder and meaningfully, setting the tone.
Your questions are fair.... Keldon did seem mysteriously down around the trade deadline, very bummed on interviews. Maybe it was just "hot seat nerves" as he's a perfect trade candidate, but I can also see him not staying eternally content as his role diminishes further when the team brings in more promising, talented, and younger players that take away his minutes.
How he takes that is a measure of his professionalism - he's already been paid life-changing money, so it's not a Scottie Pippen situation. Looking at him from the outside, having followed him since he was a rookie on the Austin Toros, I kinda have a hard time imagining him "souring" on the team and his role -- especially if the Spurs start to seriously trend upwards and win games, as they're expected to. "Winning cures all" remains true and applies here; nobody wants to be the 15th man on a tanking squad, of course.
I asked this to Spurraider and ask you too, since you brought it up; how many years does Keldon have left at that salary? I can absolutely see the FO negotiating a low-ball for his next contract. Something of a "we did right by you when we were bad, now it's your turn to sacrifice" kinda thing. Again, we'll see if and how he takes it.... But he's always seemed to value being a Spur, and that has value beyond the dollar amount.
As for Devin? No breakdown to be had - I'm tired of him!

I stopped expecting his shots to go in last season, and he frustrates me as a player. As others mention, he's also a very prominent vestige of the tanking seasons, and I'd love to see the Spurs ship him up, open up that role and minutes, and fully "turn the page" there.