To Kris or not?

I am a Gold member which makes my wife Silver automatically. Our theory, based upon the fact that we mostly travel together (same cabin etc) is that I earn the tier points and my wife's ticket is obtained in the most cash efficient manner possible.

We are starting to fly with Singapore once a year (J), do you think she should join Kris? The only real difference from a VS viewpoint is the miles. Will Kris be of more benefit to her in the future for upgrades etc.

Grateful for your opinions.

Thanks

what are the Kris rules on tier points / miles and when do they expire?

I suppose Kris would be worth it if you flew *A as well.