I will try to defent my idea. Make your self conformatable to defend yours :)
when you sugest to use a helper class to make validation i think on my current validation algoritms. what i'm doing with a helper class is
having validation method count equal to methods declaration, or at least on the same number order. Imagine that you have 50 methods and
all require validation, then you must have 50 validation methods on the worst case. Thinking optimist you can reuse some validation methods
(using some architecture or reusing same validation methods), but you will end with a regid validation declaration.
Using what i sugested easily you mantain the validation properties (because their all attributes and just looking at method signature you see
whats going on) and reuse the custom or built-in validators on the application block. The disavantage it's that the ParameterFactory facade use
reflection to get the ParameterInfo stuff.
Sorry for my Portuguese English :).