Can you tell if one board is balanced or not compared to the others?
You probably could produce a mathematical formula taking into account the different factors that obtain you points based on your wonder. It would be long and arduous to figure out, especially considering all the different ways you can approach winning the game.

I think it's important to remember that a key component of Game Design is iteration. The designers will have played the game and redesigned it so many times during development that how the wonders originally looked is totally different to how they are now. Only through actual play can you truely determine how "balanced" a certain part of the game is. Sure you can use maths, but with so many different variables to take into account the level of work involved to get to some formula that calculates power compared to another wonder just doesn't seem worth it.

If you find some wonder out the fan pack is too overpowered, you can always erata it yourself to make it more balanced. I've done this with games before a lot. You create house "rules" or edits that help to improve the gameplay for everyone involved. It's like how in Monopoly you have free parking reward you. It's not an original mechanic, but something other people came up with as a catch up mechanic.