So,

I know that on score damage 'magic resistance' equates to 33% resistance to the 'elements' basically

Does it have any actual affect on saving vs a spell or not?

Example: Does lvl 20 human warrior with -20 sv spells stand as much chance at saving vs sleep that a lvl 20 dwarf warrior with -20sv spells would?

Do naturally magic resistant beings also get a bonus to sv vs spell in addition to the lowered elemental damage?

The answer to your question is no.