Only you can answer if "X" is worth paying to upgrade to first class. None of us can do that for you.

The guy sitting next to me might have been willing to pay $350 to upgrade on SFO-MSP while I, a Plat who didn't get a free upgrade, wouldn't pay more than $25 for the upgrade, if even that. Everyone is different and as such, you'll have to make that call. I doubt you'll even be offered the option, but I guess it's good to be thinking about it in the event it does come up.