Can't help with any DP questions, but you should dress how YOU feel comfortable. The only items actually prohibited are swimwear, torn clothes, cut-offs, tank-tops and hats on men, and T-shirts with "offensive" wording or pictures.
Should add that about 75-80% of diners there wear jeans,slacks, dress shorts, polo shirts, and a blouse/sweater for the ladies. Rarely does anyone dress up more than that and park clothes make up the other 20%.