I think paintings are fine, they only really affect the first 4 or 5 levels of gameplay. After level 5 or so you'll have more than enough gold from selling other loot.
If you reduced the sale value of paintings it would take a couple more levels to get the level 4 spells, firefly, boulder bash, fireball, fire elemental, etc. These spells do make this part of the game easier, but its still more challenging than the rest of the game, and they help make gameplay more interesting. Personally, i think paintings are fine, and that they should focus on things that affect later parts of the game.