Even if Value Season had higher Fri-Sat room rates, this likely wouldn't affect Dining Plans and/or
Free Dining Promotions.
Disney, in implementing the Fri-Sat room rate policy is actually now more in line with the hotel industry in general - where they differ (surprisingly) is that they still have Value Seasons where the rates don't change. Most hotel chains have the Fri-Sat price difference year round.
The reason that would never affect dining is this - if you are in a hotel that has its own restaurant and charges different room rates on Fri-Sat nights, I don't think your dinner would cost more if you were in the restaurant on a Wednesday night vs. a Saturday night (assuming same dish, no "specials", etc.)
Disney charges the same amount for food each day of the week, and the Dining Plan is also a fixed rate. The only location I can think of where dining costs vary is at Vic&Albert - but that is because the cost is based upon the chef's menu for the evening.
So, even if Value Season eventually changes to the new room-rate policy in place for all the other seasons, it should never affect the
DDP - whether it was purchased or offered as a promotion.
Okay - I know - never say never, but I just don't see how even Disney could manage to pull something like that.