Well I did give you the opportunity of remaining anonymous here!
I like your ideas, but I also want to keep it simple. For instance I removed my homebrew stuff on Rituals for that reason. Just like Rituals give non-magic users the ability to use magic, I like the idea that there are magic scrolls out there that are 'really magic' for non-users.
I have to think about those other ideas. One idea I had regarding a failed Skill Roll for use would be that a 1 results in destruction of the scroll. Or perhaps anything -5? Again, I want these things to be valuable... valuable enough for a PC to actually go to the trouble to make some himself... that would be another issue.
As for automatic success for magic users if the scroll is 'their type of magic' that does indeed seem useful. It is sort of like a battery for spells... which could be terribly misused.