DM/PM couple here- 75% of the time, we book Y then get C+ instantly. When the deal is right, or we want F (longer flights/bad equipment), we book F.

When we get split on an upgrade, I will defer to my wife, but I get the lone empty seat most of the time simply because my wife HATES bulkheads in F.

She takes the upgrade when it’s anything other than bulkhead F though...

BTW, we are both mature adults- we can sit apart on a plane for a few hours and not lose our minds. I’ve had to give up my C+ seat to sit in a far back aisle so I didn’t swim upstream getting my luggage on a tight connection numerous times. Same for splitting up to accomodate families- not a huge deal to us...