I don't know why you wouldn't. He's done nothing but get better EVERY single year for six years now, and he's been producing at greater than $10 million production for two years straight now.
So many people over-think stuff like this. You want good players, and good players cost money. If Millsap is seeking $10 million a year, he's low-balling himself (in the sense that the book on negotiation says to always ask for more than you think you'll get) and all of the absurd and baseless conjecture that Millsap is becoming somehow selfish can go right out the window.
Millsap is a 17/9 guy who puts up those numbers without being a primary option. He's had to defer to first, Boozer, and then Jefferson. He doesn't demand touches and gets his points in the flow of the offense, often hitting jumpers when there is nothing available inside.
I think we often focus on Paul's negatives. And I'm guilty of that as well. Every player, except for guys like Kobe, Jordan, etc. (i.e. the real superstars) have holes in their games. If all Millsap is seeking is $10M, I think that's more than fair. Yes, the new CBA might hold down salaries a bit. Then, again, perhaps not. Wallace got his big deal and Hibbert is getting the MAX from Portland (if Indiana doesn't match). There will certainly be a market for Paul. IMO, if he's getting the ball a bit more, he could easily become a 20/10 player.
Everyone is so focused on Favors and a very raw Kanter. Play those guys 35 mins each - and even that's a stretch due to both having a tendency to foul - and that still leaves 28 mins at the 4 for a third player. And we knwo Paul can also play the 3 against bigger SF's. Millsap can easily still get 35 mins/per - even if he comes off the bench. Personally, I don't see Kanter as being ready to start, so I'd go with Favors at the 5 and Millsap at the 4. In fact, I'd rarely play Kanter and Favors together. Both those guys are going to get their points inside. Millsap takes his defender away from the paint with his mid-range game. So teams can't really double Derek or Enes unless they use a smaller player.
My ideal starting lineup:
C - Favors
PF - Millsap
SF - TBD
G - Hayward
PG - Williams
Favors slides over to PF when Millsap rests. Hayward slides to SF when that starter comes out (early in the 1st/3rd). Then Burks plays the remaining mins at SG.
We need to trade Harris and Jefferson for some combination of a starting-caliber SF, a young PG who can become a starter eventually, and a backup big. Guys like Evans, Carroll, Murphy, etc. round out the roster and play situational minutes or in garbage time, but those aren't the players who win games.
Jazz need a primary rotation of 3 bigs (Millsap, Favors and hopefully Kanter), 3 wings (Hayward, Burks and "TBD") and a PG and limited-minute backup. Or, perhaps the rotation becomes 3 players at the 1-2 with Burks turning into a combo guard. Whatever the case, I think Millsap at $10M fits into the plans. If (or should I say WHEN) the Jazz get rid of Jefferson, they're going to need Paul's scoring and rebounding.