Not necessarily; I think they validate having a higher sneak skill in the earlier levels when you would really like to have more money as you very likely haven't found any notable gear with which to fight with and need to rely on purchasing things instead. Lowering the value of steal-able items kind of invalidates the desire to steal anything at all, which is already pretty low considering the vast amounts of dungeon loot you get (gear, scrolls, accessories, etc).
What I might change instead is the way that you can very easily turn invisible and basically loot everything in sight. Performing illegal actions right in front of someone while invisible should illicit some kind of negative response. Naturally they should remain unaware of your presence if you simply walk by them, but I feel like a shop keeper would notice if their stuff suddenly got up and started disappearing.
