Anymore. There was a time when they hurt. Even if Williams wanted to come back at $3m or whatever, it couldn't be done for a 2nd year, because everyone knew Kopitar was getting a new contract. Hence, Lucic at 50% for 1 year, because DL wasn't starting a rebuild again.
If you want a good 20 year old, you have to trade a good 20 year old, or a very good 25 year old. If you want a good 25 year old, you have to trade a good 25 year old, or a very good 20 year old. 30 year olds with big contracts get you other 30 year olds with big contracts, or average at best 25 year olds with decent contracts. Trading either guy isn't going to greatly increase the quality of players in that younger age bracket. The cap is too punishing. The other team needs the cheap young production to offset the aging player they've acquired. And no, it's very unlikely the Kings retain 50% for years on end. It may be other people's money we're spending, but it is real money at some point.