Is the hamster cage worth $6

I don't have the pack but from what I've seen honestly no. I guess it adds a new death type to your game in honor of TS1, where sims can die of hamster disease if they are bitten. But gameplay wise, the hamster interactions are generic, cats don't even try do get to them in any way etc. They just give you some postcards and stuff that you would otherwise get but finding a pen pal in a computer. The devs gave them the spy hamster treatment but it's all a facade you don't actually get to see anything besides some explosion fx.

Also there are multiple cages, I don't know why. In TS2 there was only one and we could choose what color of hamster to put inside. In TS4 there are multiple for the multiple skins but they all do the same.