Another thing to be careful with is item to spell dependency. (i.e. worn effect, focus, clickie effects). You also have to take into consideration the npc spell lists so that you don't have an orc oracle halting progression through Crushbone after somehow having learned Ice Comet.
There are probably other things that aren't coming to mind right now, but those things listed are sure to ruin your day.
If it wouldn't be such a boring drag to players, you could actually save an immense number of spell IDs by scaling a level 1 spell all the way to level 85. I suppose that concept could be enjoyable if you scaled the boring spells (aka heals, buffs, damage shield etc) and recycled the IDs you just freed up and made some sweet custom spells out of them.
Does spell scaling even work that well? Well enough to do the above?