Good points all around. In fact, before reading your post, I was busy in the GIMP creating an example. Guess what? The freaking power failed momentarily due to a storm and I lost my work. Perhaps a sign from on high...
However, you could compromise by creating a modifier from a real surface on top of the hand-painted one, giving it a gritty touch of realism:
http://www.eightvirtues.com/sanctimonia/misc/
Glad the damn power didn't go out this time.
I basically skewed the original so it was square, then created a tileable image of the same dimensions from a different texture. I added that as a layer using the "Multiply" layer blending option in the GIMP, composited it, then re-skewed it to the original perspective. I copied the layer to the left and right to make sure it was tileable.
One thing I had to do was convert it to/from RGB/indexed a couple of times, as skewing it in RGB mode alpha blended the edges which is generally undesirable. A bit of a trick but it worked well.
I like old-school graphics too, but a little love never hurt anyone (debatable).
