Well, I guess what you said is pretty accurate. Nevertheless, from the start there is no telling which paintings are good and which are bad. How do you actively affect that is the key to a success strategy. Unfortunately from my experience of play, it is hard to see a definite way to really have influence on that...
And it is also true that in a real game, what you have in hand is usually a much bigger factor determining your purchase, especially when the price is already marginal. However with ideal play I imagine sometimes one may have to take a balance between not-so-desirable purchase for a bargain(to benefit this round) and the original plan. In the computer version I found the bidding level is generally too high or too low for this to happen, or to be interesting.
About the price, it is probably really just a conceptual exercise. It is nevertheless the first thing one would like to understand (especially with fixed values!) and I feel pretty happy that I think I have it sorted out.