What is the current cost to change outright? The route fare differential is $189 currently, so it seems the offer is capable of improving.

Without a better option, I would pay $289 extra to sit up front on either ORD-SFO or ORD-PVR, but that's a personal value proposition.

These questions are always basically two-part: (1) "is this price likely to be the best price available to me" and (2) "does this number of dollars represent a good value for the product".