By restricting gear to only WotLK items, you're not making
that much of a difference. A prime example of this would be
frityr459, who raids on his 80 mage in full ICC gear yet still pulls anywhere in the range of 35k-70k dps (in ICC, depending on the fight). Cata items actually reduce the gap between the OP classes (mages / disc priests) and everyone else.
If you enjoy WotLK then it doesn't matter what gear you use, the content will be the same. But if you want to make recruitment harder for yourself by narrowing down possible raid/guild members, that's your choice. At the very least, if you're insistent on using just wrath items, the only way you can do it "legitimately" in my eyes is if you use 1 tier lower than the tier you're raiding (Naxx in Uld, Uld in ToC, ToC in ICC) to try offset the talent/stat changes.
And like Splo said, this is a twink site and twinking is about getting the best gear for your character, so don't be surprised if not many other share your view around here.