I did minimal research on Cub Med Val Thorens. My friend Richard went there with his sister in February 2020. Based on his favorable review and that I was about to ski the Alps solo in March while Liz was rehabbing her shoulder in Florida, Club Med seemed a logical choice. For a couple the $2,500pp for a week compares to about $2,000pp in one of weather-to-ski's 3 or 4 star hotel half board recommendations, so in the same ballpark when you consider Club Med's 5 days of guiding.
For a family of 4, Club Med is not a good deal vs. any arrangement where the family shares one unit of lodging.
For sbooker's family trip next year, if it's indeed 4 weeks, I would think you would want to move around some. The Tarantaise seems a logical region for such a massive amount of ski terrain. Given Val d'Isere's terrain quality and logistics, I think it's worth trying to spend one of the weeks there. In terms of logistics, the high rise apartments at La Daille would be ideal. I have no idea what they cost. And I'm sure Les Arcs is a worthy option for one of the other weeks.
And you should consider Trois Vallees also. I always thought being in the middle valley at Meribel or Mottaret was the logical choice here. But there are really 4 valleys, Orelle being beyond Val Thorens, and I spent most of Tuesday there. And of course this week Val Thorens' altitude makes a big difference in ski quality, when it's quite sloppy below 2,000 meters. FYI there is time to ski Couchevel from Val Thorens, as we did today. Allow about 1.5 hours in transit through Mottaret each way.