I've done the math and for me I am prepared to wait out the 18 months. I know the sign on will be worth more than I could earn during the same period. I will add that I do plan to stock up on WISH cards, theperfectgift cards and VISA Only cards purchased via AMEX before I cancel. So I will get points for these now before I cancel. I've also taken advantage of other offers like BP recently so that I have a significant amount of gift cards to carry me through (eg $1500 in gift cards for BP and about $1000 in gift cards for David Jones all purchased at significant discounts). Additionally I'll still be churning just about every other card that I can during those 18 months and some of those will likely have an occasional AMEX co-card (eg. Westpac Black). And if AMEX change the 18 month rule or re-start not enforcing it I'll be back in. I'll miss getting those generous offers as you have no doubt done during the last 18 months, but I have planned ahead.
While I fully understand that this answer will be different for each of us (ie spend, FF program preference, Award route preferrence, Y,J,F or even Hotel redemption preferance etc),
the part that is most unknown for me is what the sign-on bonus will be in 18 months time. Historically Amex on various cards offers it and at other times does not. The amount varies. Sometimes they instead waive or reduce the yearly fee.
ie Explorer it may be 100K, it may be the 50K (It has just dropped to this), it may be zero (based on my last decade with Amex these joining boni come and go). It may also be boosted with a referral boni, though again these come and go.
On the other hand retention boni also vary.
In my case it would be, based on the current rules for 18 months:
+ Possible new sign on bonus
- possible rentention boni for Explorer plus Edge x 1.5 (ie as is 18 months if you intend to keep doing this process
- loss of points earnt from spend (A drop from an average of say 2.5 point per $ to under 1 - and in my case as I value KF points to be worth a lot more than QFF points this is even worse if it is losing 2.5 KF points and only gaining 1 QFF Point)
And then loss of additional cashback or point spend promotions (which at present adds up to a sizeable amount)
So 60K ( in a range of 110-0k) gained but possibly losing
-45K (maybe more or less)
So that is a gain of say 15K (110K max to a loss of 45K) and then have to factor in less points earnt over 18 months (some prepaying by buying giftcards and prepaying some bills will reduce this).
So a best case scenario for me is about a spend of $75000 over 18 months which I exceed by a fare margin.
If I factor in earning in QFF points instead of the to me much more valuable KF points (even card spend via Velocity would be achieved at a much lower rate to gain KF points) then that spend is is less than half of that.
Current case scenario a spend of about $10,000 over 18 months. And again factoring in KF points, it is less than that for me.
And if no sign on bonus is there in 18 months, then that is a major points loss with an unknown waiting period before sign on points are there.
So in my case (and again this is different for each of us) it is much better to retain than to cancel. Also in terms of risk, retaining for me provides a guaranteed source of KF points vs a possible, but unknown future amount of KF points.
OTHER MATTERS
If a couple then one can cancel one set of cards, but still earn the higher points rate, but not the bonus cashbacks (I am ignoring supps as I assume that you will already have to max cashbacks). So for couple cancel one set of cards may be worthwhile.
Warehousing. If one has a large points stash then for some having to move this to an airline program may not be desirable. This a factor for my circumstances.
