@SouthFayetteFan -- I wish I had more for you, but like
@striker1064 said Amex's new pop up is a mystery. There are DPs of spending $5 on a slice and the pop up goes away, and then there are DPs like yours where you spend hundreds or thousands across Amex cards and still get the pop up. Then there are DPs where folks get the pop up when trying to apply for one card, but no pop up when trying to apply for a different card. Then there are the DPs of Amex denying a bonus even when you didn't get the pop up. It really makes me wonder how sophisticated Amex's metrics are and whether they track all their customers with some kind of internal rating or score, e.g., a la Black Mirror or The Good Place. Assuming that, and the fact that you two burned through Amex's cards ~two years ago, your wife may be in a much deeper hole than most, and who knows how much more spend she'll have to throw at Amex to bring her score back to par. Like you said, you've already "wasted" $800 in spend that could have gone towards MSR on another card.
I have have no idea whether to fish or cut bait. Do you just get the Schwab Plat now and cash out even without the bonus, or hold on to the MR (hope things improve in 2019?) and try again for the Schwab Plat come triple dip season next year? I don't know if time (relationship history?) will change anything for the better if you're going to cancel the Delta and pull back spend on the remaining Amexes (but it sounds like you'll at least put grocery spend on the BCP and miscellaneous spend on the BBP). If you get the pop up next year, what do you do then? What's the time value on those 200k MR? And of course, as you pointed out, cash value at a 1.25x redemption vs. gift card value on which you have to take a discount if you tried to liquidate. I guess it sounds like I'm leaning towards a bird in the hand is better than two in the bush with the Schwab Plat cash out now, but I'm assuming your wife's situation with Amex doesn't get better next year and you're just ready to move on from Amex. Because, like you said, it probably won't help your wife's relationship with Amex any to sign up for one of Amex's premium cards only to put reimbursable expenses on it and cash out MR, then cancel.
I think
@jhoannam makes a good point that the slot the Schwab Plat will take up is a valid cost to consider. I think at 2/24 in slow churning mode, it might not be a major factor, but you know the roadmap you want P2 to take better than us.