I have about 22000 tier miles/29000 skywardmiles on skywards program and I have another upcoming trip from JFK to DBX next month.

Is it worth trying to be a silver member by either buying a few thousand points or by transfer points from AMEX rewards program? I am not looking to upgrade on the outbound portion. I was told I need 30000 miles to upgrade from econ to bus class on the inbound leg on my previous trip. Is this correct?

And if I buy or transfer AMEX points, do they go towards tier miles or just skyward miles?

If you have any more info on this, any advice appreciated.