Stoudamire is a worst-case scenario, but the point is you have to be very careful when offering big money contracts to aging players, particularly when they've only had great success on one team, in one system. I think people forget how young he still was when New York maxed him out. Take a quick look at Stoudamire's career stats and tell me the dropoff from age 29 to age 32 doesn't scare you to death. This is a guy who made 6 All Star teams by age 28 and was consistently putting up 20 and 8. He was completely done at age 30, not 33 or 34.
What you fail to mention is that Phoenix essentially played gimmick-ball last season and allowed Dragic to do whatever he wanted because Bledsoe missed half the season and their best excuse for a #2 scorer was Gerald freaking Green. Dragic wouldn't even be a #2 option on Sacramento, he'd be a distant #3 and probably wouldn't handle the ball a lot more than he does now with Cousins and Rudy both being high-usage scorers who like to create from the high post area. His success in Phoenix last season is unsustainable even on a team that needs a high usage PG, which we are not.
More importantly, Dragic played like an All Star in exactly one season to date. That does not make him worthy of a max contract or anything close to one. With the other needs we have on our team, devoting a huge chunk of salary to a PG who isn't substantially better than the guy we already have all but guarantees we won't be able to fill the other holes we have in our roster -- who is your starting PF, backup C, backup SG, sixth man? Dragic doesn't help to fill any of those holes. You mentioned yourself that an NBA player's prime is typically their mid 20's to early 30s. Dragic is going to be 29 next season and he's about to wrap up a season when he played worse than the guy we already have. This is a bet you want to take? Because he played one season in a PG heavy offense, nearly made the All Star team, and won Most Improved player in his age 28 season? His career averages are 12 and 4.5 and people want to bet on one fluke season sustaining itself into his 30s? That's beyond crazy.
Look what happened to Igoudala after he signed a big contract with Golden State. In year 2 of that 48 million dollar deal he's currently averaging 7 pts, 3rebs, and 3asts off the bench. At age 30 Deron Williams is borderline untradeable in year 3 of a 98 million dollar deal he signed with Brooklyn. Stoudamire has been the worst contract in the league almost as soon as he signed with New York. Josh Smith was so bad in Detroit they're now paying him 13 million a year to play for someone else. Gerald Wallace signed a 40 million dollar deal with Brooklyn at age 29 and he's been awful ever since. Remember even our own Peja Stojakovic had exactly one good (not great) season after signing a 5 year deal with New Orleans at age 29. All of these guys signed their big contracts at around the same age as Dragic and they had much stronger track records at the time. Are there exceptions? Sure, but the guys who continue to excel as they age into their 30s are almost always multiple All-Stars and Hall-of-Famers. The track record for borderline All Stars signing big money deals in their late 20s is a horror show.