If he got Plat thru Amex, the buy-up to CP may be (significantly) more expensive. The buy-up fee is based on PQM earned, and not status. If he flew less than 50k PQM for example, it will cost $2199. So this should be factored in.

I personally think every bit of status helps, the higher the better, but the need to split the wife from the PNR might not be erased with cp status as it all comes down to available upgrade inventory. They seem to be releasing inventory one seat at a time lately and not sets if 2, on lots of routes. Being cp still won't turn 1 seat into 2.