As for when to go, IMHO it's best to go when you can meet many of your C-Brat buddies there which is the first Saturday and/or Sunday.
As for reduced price tickets, in past years the previous factory was able to provide some comped tickets to C-Brats. However, given the state of the economy and especially that relatively fragile state for boat builders, I anticipate paying full price. However, there are sometimes $2-3 off coupons online or at some local stores. Also, if you buy online, you get free parking. Finally, I seem to remember in past years that on one of the week nights, ladies get in free (although I don't see anything like that listed on the boat show site this year).
