>Taking these edges will *never* gimp the original form of the
>spell?

Correct. At worst they're useless.

>Let's say I'm an Outlander Invoker and take Scalding Geyser.
>My Geyer's were previously hitting at 100% efficiency(Let's
>just assume spellcraft never failed on any cast), I now take
>Scalding Geyser. Now if I geyser someone that has no
>protection to fire whatsoever, but is not vuln to it, is it
>hitting for greater than 100% of the original damage because
>it has an added fire element of damage they aren't protected
>against?

Correct. You get some extra damage.

>If so, now when I hit an unprotected felar is it the original
>amount of damage + another % + vuln? Say 100+10+10=120% just
>for the sake of numbers being thrown around to make sense?

If you're throwing scalding geyser against someone with an uncovered fire vuln, you get extra damage on top of the usual extra damage for the edge. Similar idea with chilling geyser and a cold vuln.

>Conversely, what if I take Scalding geyser and have to fight a
>fire giant, and want to use the spell. Will he just be immune
>to the fire part and I'll be hitting as hard of geysers as if
>I never took the edge?

Exactly. You don't get the bonus "heat" damage but you still do full normal geyser damage.