I wonder how much the opponent really gooses home local TV ratings though. Obviously this is exactly why things have to change, but the reason Comcast paid the Phillies so much money (and gave them a % of the network) is the overall value for carriage fees, subscribers, pregame and post-game advertising and even the whole digital operation (including the streaming now), not what advertisers pay overall to reach what is still a fairly small number of viewers (like, just as many or more people watch news, game shows, and prime time TV).
The Phillies led MLB last year with around 325,000 average local viewers, but is the gap really that big for a sexy opponent or great opposing player? I would think the day, time and competition from other sports (except from June-August) is a bigger factor. Last year's most-viewed game was actually the Nats, but they had nothing to do with it - it was Opening Day. That was 560,000 viewers and presumably those 200,000+ people are the sort of fans who only watch a few games a year (and then playoffs).