I think its time that the rare scrolls were looked at again. Now that we have a level 25 game cap and Epic Destinies, there are some scrolls that are simply not as powerful as they used to be. The last time the scrolls were really looked at, iirc, was around the time that spells were adjusted. There have been some scrolls added since then, mostly for Artificers and Druids, but the lvl 8 and 9 scrolls remain unavailable except as drops.
Take for example the lvl 8 and lvl 9 summon monster. Are these creatures so powerful that they cant be sold in game? Now granted, some of these spells are still extremely powerful. Otto's irresistible dance, for example. However, I think that several of them could be safely added to vendors.
One idea to help control how powerful they are is to only add them to certain harder to access vendors. For example, a vendor in the Portable Hole and Eveningstar would be a good way to control them.