Disagree. Some monsters should have a form of SR. It forces players/characters to think outside the norm and come up with creative ways to kill stuff.
Disagree here too. Same reasons as above. Forces players to think of creative ways to bypass or deal with the situation at hand.
Except it doesn't...ohh we tell ourselves that little fiction, because from a world building standpoint having Mind Influencing spells not effect Undead might make sense, but it is a bad design path, which is confirmed by the example of history.
Players like powers that work. If a power has a large chance of failing, then said power is not used. This is common sense, if your TV only turned on 50% of the time, you would quickly either get a new TV or adapt to not watching TV, but most likely you would not sit there and make plans to watch a particular show on your TV, knowing you have a coin flip chance of being able to watch it.
Categorical rules like Mind Influencing spells do not work on Undead, Lizards, and whatnot are like the TV not turning on. Spell Resistance did not encourage creative play, it encouraged people to (at least in 3E) to find spells that were not subject to SR, like the Orb line of spells. It in effect made Conjuration specialists and Druids, (whom had a large number of truly wicked Conjuration spells on their list) able to do more sheer damage than an Evocation specialist because they could just cherry pick powers that bypassed the extra roll required by SR.
It did not encourage creative play, it did encourage exhaustive research instead, which can be unfair aspect...I might have more time to research and read material as a married male without children, then my fellow player that is finishing up law school and just recently had twins. Remember the hobby is graying.
Moreover, I would also posit that Categorical Keywords, while they can make for a logical system, in many ways reduce the ability for creative play. I think you want a system that encourages a player to say: " hmm we a trying to enter the Temple of the Rat via the sewers, so I will take Lower Water" and try to use Lower Water on the water elemental the group encounters. Yet in 3E and 4E often times you would find valid Keyword reason to shoot down those ideas because of a logical inference of the rules.
I would posit the better way to allow for someones powers to face a difficulty boost against specific creatures is to not categorical nerf a set of powers, but to write the resistance into the monster stats.
If you want your base skeleton to be immune to charm spells because skeletons have no minds but follow orders only w/o thought...write that into the monster stat block. If you want a Hag to be highly magic resistant, give the Hag higher saves vs Magic...do not nerf a whole group of spells.
Let the TV turn on!!