It would be a shame to see this FO cheapen out on not signing FAs. This team is far from a contender and we need help everywhere we get it. Roster improvements are necessary for the Kings to get better. Look at the Warriors 2 years ago. Are you saying they should've passed on signing KD because Klay, Draymond, and Steph were due for a contract extension soon? I know we're nowhere near as successful as the Warriors nor will we get KD on this team, but you don't have to worry about spending big money on FAs as long as you have the cap space.
In terms of money and extensions, the real discussion will come down to Buddy vs. Bogdan. Both are the same age and both play SG. As a result of their overlapping position, the Kings won't be able to pay both players starter money... which is exactly what Bogdan will be looking to get paid.
Until I see some evidence that Vivek/ownership is willing to pay the luxury tax I am going to assume that doing something like extending Barnes (at say $22 million per or so) and throwing a max deal at Vucevic is going to mean losing one of Hield, Fox or Bagley down the road.
The Warriors were in a very different circumstance to even be able to sign Durant. They had the best shooter in the history of the NBA and a league MVP signed to an absolute sweetheart deal due to his previous ankle issues. Not to mention Klay and Draymond signed under a very different salary structure that allowed them to move enough salary to accommodate KD. But above and beyond that, they had an owner who was willing and able to pay the luxury tax of $51 million this season. And it's only the likelihood of Durant leaving that will save them from a huge repeater tax.
If Vlade really believes in the young core he's assembled, he has to be preparing to keep it together long term. And save for a new ownership group with deeper pockets I think the only way to do that is to carefully manage the salary cap year over year.
But above and beyond that, I may be in the minority but I see Bagley's best position in today's NBA as being as a versatile 5 man. I don't see a frontcourt of he and, say, Vucevic being all that successful due to spacing issues. Add in Barnes needing some post up opportunities and things get clogged up quickly. Maybe a stretch five along the lines of Brook Lopez (but not Lopez because the Bucks know how key he's been to unlocking Giannis this season) would work alongside Bagley at the 4 but I don't know what options there are out there.
To me, the best bet for the Kings is to give the young guys as much leash as possible and use the cap money to upgrade the bench with a big bodied center and more scoring punch/versatility from the wings and backup PG.