Well the "Happy Wife, Happy Life" philosophy says "Gift your wife the FO status".

But in your situation, I'd lean that way anyway. It sounds like your wife travels enough that she'd get some benefit from the gifting of FO status. FO benefits are enough to take flying/traveling from annoying and awful to "bearable", which is a huge difference. Yes, she could get some of the FO benefits by getting a DL branded AmEx, but there are still plenty of benefits that being an FO gets that just being an AmEx holder doesn't, including as you mentioned, access to preferred seating, which includes exit rows (and C+ at T-24), but also priority check-in lines (either SkyPriority or dedicated FO check-in lines, depending on the airport). And she'd have outside shots at FC upgrades. She'd also have better IROPS protection and better phone line priority too, which can be very beneficial.

I personally go with the 4 RUCs but my wife has made Medallion on her own the past few years so there's no need for me to gift her status. Remember, if you have enough miles in your account, you can also use miles to upgrade. Mileage upgrades come from the same inventory bucket that the RUC requires. The only difference is I think RUCs can be applied to any Economy fare bucket (except E) while mileage upgrades I think require T or higher. Also, I've been finding RUCs more difficult to use in advance as of late as DL is looking to sell more FC seats, so with that, you may well get more use out of the gifting of FO status to your wife.