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.
They should have interesting things to steal, not just numerous amounts of valuable garbage which you can sell right back to the owner half the time. You don't even have to go invisible; you can stealth right next to someone and steal things practically right in front of them. But I agree, invisible stealing could have a humerous threat from the shopkeeper. Guards and other people who catch you sneaking around should become suspicious, perhaps increasing their FOV or arresting/calling the guards on you after so many catches.
But the simple fact is, this game will never really have good stealth or stealing mechanics. They would really have to increase NPC walking patterns and the number of NPCs in certain areas to actually make it a challenge, and that would probably be more tedious than satisfying. Good stealth quests and environments would be cool, but I just don't see Larian spending their time doing that. Reducing the price of paintings would at least help the economy, if just a hair. I don't think beginning game economy would be harmed that much from taking out paintings.
