Plenty of guys are going to be worth an old salary cap max deal under the new salary cap.
I think that this point gets overblown a bit. If Green gets the max this off-season, his salary in the second year (when the cap goes up) would be around $17.2 million, I believe. If the cap is at the projected $88 million, that's still spending 19.5% of your cap on a (very good) role player.
I agree that NBA teams will overpay this off-season in light of next year's cap increasing, but I'm not sure that it's smart business.
Golden State is paying a comparable amount of their cap to Andre Iguodala, who also at this point in his career is a very good role player. It seems to work with their budget, or at least it has so far.
I do think you're overestimating the 25% max salaries by a little (and if you're not, it's because the cap is on the high range next year, which means the 2016 cap will be closer to $92 million rather than $88 million). Assuming a $66.5 million cap, I'm getting a $15.6 million salary next year, and a $16.3-$16.8 million salary in year 2, depending on the size of the raise (which will probably be no more than 4.5%, since Golden State can just match another offer). I think it will be closer to 18% of the cap.
Furthermore, you have to consider Golden State's situation -- a) they're willing to go above the cap, and the luxury tax in 2016 will be somewhere around $110 million -- $16-17 million for your third or fourth best player doesn't sound as crazy when your payroll is that high, and b) they got Curry on a great deal, which subsidizes their ability to somewhat overpay other players through 2017. Finally, Golden State is over the cap next year even if they let Green walk and completely rid themselves of David Lee's salary. Their ability to replace Green is non-existent -- letting him walk because you'd rather pay him $12 million (what Iggy's getting) instead of $16 million is focusing too much on the long-term when you can win a championship in the short-term.