its the exponential gain that has MR screwed. 20% bonus to goblins so they can fit in? elves with 0? clerics with mr penalties...?
Literally goblins are really the only ones that really see a heavier effect of about +3 wisdom with 17 wisdom. Most other races have 0% to 5% is like adding a 2-3% overall percent resistance to wisdom. Doesn't change much IMO and it's mostly based on wisdom.
Goblins are meant to be a resistance type fighter race, and they will continue to be anyways. It does need lowering as I talked about though. Yeah there will be class MR, classes like druids for example are simply too OP as they obviously focus Wisdom to maximum, making them really good at physical but then also magical. Granted, there could be some changes, but they'll continue to exist.
it should be added as racial bonuses (if your race has 5% mr it just receives 5% less damage from magic) and bonuses from armor . make armor have 2 stats AC and SR (i.e cloth adds 9 armor and 25 SR(spell resistance which offers mitigation identical to the way armor affects melee.)) melee characters can choose heavy armor which offers less SR or choose a lighter armor version which increases SR. im pretty sure ive posted this before..
Having racial actually add 5% Mr for example is probably a good idea rather then a multiplier which might help balance reasons (So as you say it would add a static value instead of a multiplier which could help.) However, with SR on armor I think you add a huge balance issue and you'd have to completely revise the way characters work. You actually grant medium class users like slayers or barbarians SR just because they use medium armor. Paladins should have the choice of being good with both using higher wisdom (at least thats what i believe) but I think this would make it worse as obviously heavy armor would make them weaker to spells.