Buying an existing stadium would be a very big step and not something they've been involved in before. They built Waverley and were the major partners in Marvel.
I can't see how buying Kardinia Park would be beneficial, Geelong have a great deal there and always will have because they're the only tenants on earth who could ever fill the joint, and they are incredibly powerful in the area in a political sense.
Ballarat? Maybe, but it's already being upgraded and not sure what more they would get out of it - I don't know that any club is that interested in relocating there full time.
Perhaps this is a new strategy to invest their surplus cash but I'm with you I don't see any logic in buying Kardina Park other than it would be a nice asset to have in the future. I don't really see what else can be done with it to generate more return.
Ballarat makes a bit more sense in that they could send some games there (no full time clubs), but I still don't totally get the strategy.