SR was not to allow several things your asking for, its to help counter the power of the wizard/cleric.
Well yeah... or to protect against any caster for that matter. What am I asking for besides that? SR is pretty simple to understand.
Your computations are off, there is already an advantage for wizards in this, and it takes a special build process to counter this, which got the nerf on bigbies which made it useless because a few people managed to figure out the correct math and build. Which was silly.
What computations are that? And if there's already an advantage for wizards, then increasing the SR shouldn't be a problem. However, the fact is, this would affect mages the least... especially given greater spell breach and Mords.
Dont mess with SR, if anything remove it on other races, its not ment to be given out like candy.
Given out like candy? Try reaching level 40 on an ECL 3 subrace...
A level 30 wizard should not have advantage over a level 40 pure monk, monks are caster counters. They will fail SR.
Well at 10 levels lower, of course a wiz is going to fail vs. a monk... a pure level 40 wiz on the hand won't very easily. Not sure what this has to do with the discussion though.
One the reasons why I'm thinking it would be a good idea to allow pure class ECL 3 folks to have SR = level + 11 instead of +5, is it puts pure casters and pure builds on a equal and level ground. Likewise, a multi-classed caster's SR penetration is matched with a multi-classed ECL 3's lower SR.
So for example, my level 40 Githyanki Pale Master would continue to be easily hit by spells from Summoned Dire Halfling (who has 100% chance of success vs. my SR), but not easy from a multi-classed cleric like Matrix or Celorn...
But if I built a pure classed level 40 Svirfneblin, it would be cool to take the penalties of being pure classed in exchange for higher SR.