I agree the fair could be a bit more lively. There are enough sims showing up, but there should be more activities. Something as simple as music would add a lot to the all over feel. I just attended my first fair with a nice apple just to check it out. He got 2d place (do NPCs never bring oversized stuff?). My teen won §250 + an uncommon choco treat + ribbon + his apple back. I think that was a good pay out for a nice quality apple, LOL. Agree to those upgrade parts and other rare stuff.
At fairs I think the stall give discounts, so if your sims are counting their simoleons it would be a good occasion for storing up. At least the grocery stall pays more if you sell to her during the fair. Not exciting activities, but an excuse to visit the fair.