How unbalanced are my rules for scrolls?

[NigelWalmsley]

My primary concern is not letting any wizard or cleric become able to do everything better than anyone else.

The easiest way to do this is not to line-item veto every awesome thing casters might do, but to give non-casters things they can do that are awesome. Nerfing things tends to piss people off, particularly when there's splash damage to something they wanted to do that wouldn't have been problematic (which is pretty common).

They're pretty straightforward gp-for-spell rules, so they won't be any less balanced than spellcasting already is.

Depends what you mean. It's true that a Rogue who periodically UMDs Wands of Grave Strike or Scrolls of Knock is not really any more of a problem than a Wizard who casts those spells. But it's not true that there are no balance problems caused by charged items. The treasure you get from encounters is enough to allow you to keep buying scrolls that are high enough level to win those encounters, which destroys the game. Charged magic items are one of the biggest balance problems in D&D, it's just that people often don't notice because players tend to be extremely irrational about using them.