There is something philosophical, no doubt, in the fact that this hinges on your definition of "reality."
There is no rule that limits this percentage to unity (100%), and all of the mathematical operations in which it is used work fine with percentages above it. So from that end, realer than real could be a thing.
The question, then, is whether "reality" is a game-term, defined exclusively by the rules of the (Shadow) spells, or not and defined as in real life. If the former, then realer-than-real spells are possible, and succeeding on a saving throw causes you to be more affected than failing. If the latter, it's a matter of what you think reality is; whether or not it has some essentially fake quality that something can be more real than it.
Strict RAW, it seems to be a game term, so your damaging spells deal more damage. Your non-damaging spells always work.
And it doesn't matter because every DM should ban reality-improving effects, particularly the shadowcraft mage, on sight. (Why? Because the spells are too versatile like that. It's basically spontaneously casting the entire Sor/Wiz list. Plus a shadowcraft mage can be optimized to cast any spell, from a cantrip (silent image used as shadow evocation for miracle).)