So suggests a fan (forgetting about key farming) in the B.net forums, which draws a philosophical reply from a CM.
What we didn’t want to do, however, is make players feel like they absolutely needed to play at the higher MP levels in order to get the best rewards. This is one of reasons that we didn’t add in Achievements for Monster Power, too. We wanted the primary motivation to be the challenge and finding a level that you enjoy. I gather from your post that you feel the bonuses given for challenging yourself aren’t really worth the effort, but my question is what would you change about it? (Keeping in mind that we don’t want to force players into the higher MP levels.)
So is MP0 really the best for everything? Yes, actually. It’s certainly the best for item hunting, providing you’re in Act Three or Four; in Act One or Two MP1 seems to be the best option, since it so greatly improves the odds of ilvl 62 and 63 drops. The fact that MP0 in Act Three is much easier than MP1 in Act 1 or 2 goes some distance towards explaining why many players consider the Act 3 “Alkazier run” the best item finding course in the entire game.
If you want much more detail on this, bring a snack and dive into this mega thread. I newsed it some weeks ago, but it’s grown greatly since then and it’s full of great info, with mathematical proofs of which MP level is the best. The general (though not unanimous) conclusion from that thread is that MP0 is the best choice for almost every class/build, since the blazingly-fast killing speed allows for more runs and kills in the same amount of time, which beats the slight bonuses to Magic Find from the MP bonuses.
The big exception is, of course, key hunting, since there the bonus from higher levels of Monster Power are huge and very tangible. For keys, and especially for the demonic organs, you want to play on the highest MP level you can hack; a sweet spot that will vary from character to character. (Or even higher, and ideally in a party for the added killing oomph.)
Incidentally, there’s a great deal of debate over how exactly the Bonus Item Drops function. They’re granted for playing on higher MP levels on Inferno, and most testers think the figures listed in Blizzard’s infographic (seen below) are much too low. Competing and overlapping theories abound (since no one but Blizzard can dig into the game code to find out the exact answers, as fans did with the D1/D2 programs) but there’s some consensus that the listed percentages might be checked when anything drops, (instead of just when an item drops) including potions, gold, etc. This would greatly increase the total number of “bonus” items found per game, and I encourage you to check the forum thread for the full debate.
It’s a side point, but I strongly doubt the “that’s why we didn’t make new achievements” part of the blue quote. Blizzard didn’t make any Achievements for Monster Power because the Achievements are handled by some Battle.net programers who are all busy with Pandaland and SC2HotS beta stuff. Or at least I hope so, since I can’t think of any other reasonable excuse why we didn’t get achievements added for Paragon Levels in v1.04, or anything at all (Monster Power, Infernal Machine, etc) in v1.05.