I don't think it's overpayment, if it's $10M thats going to be below the value set by the market. Whether it's smart or not is a different matter and it depends on what path the Kings choose. If they are just doing it to maintain ticket sales, it's beyond stupid. If they have a short term re-tool plan then by all means do it. I think most here just want them to commit one way or the other.
Both Kopitar and Doughty could certainly be traded in 3-4 years. Yes, they'll have big contracts but the cap will be increased so they will be a smaller percentage. Neither of their play is going to fall off a cliff, they both have attributes of guys who are effective late in their careers.
Personally, I resign Doughty and have a target of the 19-20, 20-21, and 21-22 seasons as a window to be back into contention. If things aren't looking like they are going to work out by 2021 trade Kopitar and Doughty, who will still hold solid value. Brown and Carter will only have a year or two left, Toffoli will likely have moved on, and Pearson will be hitting UFA. As long as the price isn't outlandish I don't think Doughty signing will hurt the rebuild as he's not going to be playing out that entire contract with the Kings anyways.
The main reason I think a retool is the best option right now is it's going to be difficult to completely wipe the slate clean compared to a few years down the road because of the reasons above. At that point you turn the team over to a young Vilardi, Clague, or whoever gets drafted/traded for and work towards a core of similar ages peaking around 2025-2029. Might as well take one last shot rather than have a few guys around that will do nothing but make draft positions worse.