Actually, uh, I'm not so sure.
I'm testing a lot (like... A LOT) the throwable weapons (grenades and scrolls) and I was really happy to see that Ambidextrous reduce the cost of scrolls by 1 too.
The thing is : I have absolutly no idea how the Scrolls spell damages are calculated. I have no clue. The only thing I know is that Scroll damage is -at best- garbage compared to the real deal.
When I throw a 1AP Fireball with a scroll + ambidextrous => 80 damage (scale with character's level only)
With the exact same character, when I cast a regular 2AP fireball => 210 damages. (scale with INT, Pyro, AND level)
Maybe there's something I'm doing wrong, but DAMAGE grenades and scrolls live in their own little world and doesn't scale really well. Mostly Scrolls, because grenades still scale (badly) with pyro, warfare, etc depending of their elemental damages.
(Savage Spell and Huntsman works with grenades and scrolls tho. Yep, grenades can CRIT. And you can still use Ambidextry while using a bow/crossbow. So that's a plus.)
Same problem with the skill Explosive Trap who seems to scale only on your level. Maybe Explosive Toybox (scoundrel skill) too.
Effect/status/utilitary scrolls and 'nades are fine, obviously. And the 1AP teleportation scroll is sweet. But man the damage grenade/scrolls needs some tweaks. Or maybe there's something I'm missing.
...Uh, but it's maybe a 'lil bit offtopic. I should start my own "What's the deal with Consumable weapons?"