Thanks to Jeff over at his Gameblog for posting about the Holmes scroll rules.
I've just edited my magic item lists to include "special scrolls" where the treasure maps are on the normal tables. Here's the listing I did for these.
Special Scroll: This item is like a spell scroll, but it may be used by any spellcaster. It always only contains a single “spell” but that effect duplicates that of one wand, potion or ring with the following exceptions: potions of delusion and poison, rings of regeneration, spell storing and wishes, wand of misdirection. The effect is equivalent to that produced by the potion, ring or wand for range, duration and effect, with “always on” ring effects lasting 1 Turn.
I like this, as it allows for some wacky scroll effects, and allows classes to cast things they normally wouldn't.
As for Jeff's own idea that a player may wish to copy the spell into a spellbook, I'd allow it on a case by case basis, or as he then suggests, use it as a basis for spell research. I think I'd also allow that for the Protection scrolls. How cool could it be to have Protection from Undead or Detect Metals in your spellbook?