Should not be tied to price of game regardless. Rarity has simply given some games a higher rating than they warrant. People want what they can't get, those with it give it higher ratings than warranted cause they wanna drive the price more and the game isn't available to enough players to get a true representation of the game - particularly lastability.
Does MM remain an A with MMr or will it drop to a B? Another 2 to 3 thousand Cactus Canyons will certainly see its rating drop long term. Sooner if its not launched as CCc.
Same deal with "pin snobbery". As previously noted in this thread - artificial positive ratings are attached to B/W DMD machines over Stern, Data East, Sega. Is Junk Yard or Bride of Pinbot really better than an Avengers LE or even Rocky & Bullwinkle??? Debatable at the least in my books.
At the end of the day - its all subjective. Too many "followers" when it comes to what games are good and which are bad. Make your own list and use it. Who cares what someone else thinks is A, B, C, or D.
The artificial bubble based on rareness of a game has popped/is popping/will soon pop so expect those ratings to level out. The writing is on the wall. 3 manufacturers putting out good games is going to ensure prices drop on A and B pins and I think ratings will level out longer term on them too. Already has here. Games are taking a lot longer to sell than they used to. Bets are off if MMr is a flop or JJP flounders though.