I have showed poultry in the past- Call and Runner ducks, plus gold pencilled hamburghs bantamns, silkies and seabrights.
I'd say it doesn't really make a difference financially to show or not. You have the cost of entry plus petrol to get there, and if there is prize money its very minimal and doesn't cover costs. If you have good show stock you can sell them, although how much more you get for them is maybe debatable. If you have good stock and you put them into the sale classes at shows, people will be able to tell they are good birds and you will get more for them whether you show or regularly or not.
I took my other half to a chicken show this year (Scottish National) and he was genuinely amazed by the number of people there, and of the age and variety of people. He was expecting every person to be over 65 with a flat cap on. They can be a good laugh, and you will end up swapping birds with other breeders etc. I've never paid for gold pencilled hamburgh yet in over 10 years- I was given the first three by a friend who bred them, and then you just end up swapping cockerals or hens around etc.
Beth