Not a fan of trading Spence, especially with how Doughty has looked since returning. Granted, he's still getting back to speed - but trading Spence would be a mistake IMO unless it's part of a larger package to return a true different maker (Ex: a player like Barzal, Tuch, etc).
It'll never happen but honestly, the smart thing to do is probably give Doughty the rest of this season to see if he returns to form. If he doesn't, it may be time to sit him down in the off-season and discuss options for the future. If the Kings were to trade Doughty at 25% retained this offseason they would likely be able to do so - and could potentially get a half decent return given his cap hit would only be $8.25m with the retention.
That would give them the flexibility to re-shape this blue line and build for the future centered around Spence, Clarke, and Anderson. At that point, they wouldn't have any big contracts on the blue line locked up long term. They could re-sign Gavrikov pretty easily if they chose to go that route - or they could try to sign/acquire a different big-ish name defenseman to fill out the top 4.
Hell, maybe a team like Toronto is looking to make some big changes in the offseason assuming they come up short in the postseason again? What if we saw a Morgan Reilly / Drew Doughty swap? At 25% retained Doughty's cap hit is hardly much larger than Reilly's and that would give the Leafs that minute eating right shot D man they've been looking for for years now. Plus they wouldn't be tied to Reilly long term. I've heard Leafs fans may be souring on Reilly but he's still a good player - maybe just needs a change of scenery to get going again. Obviously super unlikely but just an interesting idea.