There are some paintings my Sims have done at low level that I was never able to do again at a higher level. A lot of these are stick figure or cartoonish pictures. My favorite one so far is of either 2 dogs or 2 cats (I cannot really tell) sitting next to each other sharing a spaghetti. It was a Flirty painting done at a low level. At mid level, my Sim painted a Flirty pic of the llama and freezer bunny sitting together on a hill in the sunset. At higher level, my Sims only seem to paint the same few paintings over and over again, never these stick figures. It seems like at some point your Sims are 'too talented' to paint these any more.