As an avid user of UMD (love the flexibility it gives) I would rather propose a different approach to the problem.
UMD is powerful because it lets you use scrolls (access to buffs and spells on classes that shouldn't use them) and equip gear you shouldn't be able to equip (alignment restriction, class restriction).
Scrolls: they are a relevant money investment, for sub-par spells (low DCs for offensive, limited duration for other scrolls) and they are janky to use in any heated situation unless you plan carefully (i.e. buff before engaging). Arguably, loads of potions and other consumables can help you achieve the same result in most situations. Hence I do not believe touching scrolls per se, which also have a high chance to fail without relevant investment in UMD, would be necessary. Keep them as it is.
Alignment restriction/class restriction: starting from the idea I think this is a non-issue as for most powerful items you need, again, relevant UMD scores to be able to wear them, probably people think that it gives too much versatility in equipping different items that you shouldn't be wearing. You would be able to equip them with the right alignment, so alignment restriction is not really a factor here. Class restricted items are the real issue.
Considering this, why not placing a maximum budget of class restricted equipment one can wear, tied to UMD scores? This way you could access only a limited amount of gear at the same time (based on item value), instead of being able to equip everything at once.
This said I still think any UMD buff would warrant a rogue buff for higher level rogues (6-8+?) To compensate for the hit they would take. Rogues are all about flexibility, and UMD nerfs remove flexibility from those who invested heavily in a rogue build. But this is likely a different topic.
Just to understand @Madame, do you have examples of situations where UMD usage gave unfair advantages to some classes? I would try to bind these situations to real cases rather than hypotheses as sure, UMD is a very good skill, but it's not something that gives an absurd edge in my opinion. Not when casters can use ninth level spells without DP checks
@MAB (edit) in a previous RL server I played into there was a single script that gave you a non droppable curse item that cyclically gave you -2 to a stat, randomly, until you got rid of it at a holy place. Just a cool idea on cursed items.