I think that as long as the NLLs keep flowing, there is no point in keeping these biz plats open. I had two that I got full AF waivers with no spend as a retention offer, which ok, clearly those made sense to keep. But when Amex is willing to let me open another one for 150k points, why bother putting the same amount of spend on an existing one for a fraction of the points?

Also, my view on retention offers is that at a high level Amex decides what's available at that time, and then you're eligible for one of the options (or not). I don't know how their system decides who is eligible for what, but a new card bonus is always going to be more valuable than a retention offer. I didn't even ask about a retention offer on my last biz plat, just said close it. keeping a running 4 of these at once is tiring enough.

As for average Amex age, the personal side of my account is very stable, mostly because I have what I want. That side I'll do more farming for retention offers.