It doesn't have to be a step back for Cody. The angle isn't doomed to a one-off mid-card battle to give the Golden One one last hurrah. If I've learned anything from being a fan of pro wrestling, it's that anything has the potential to be a WrestleMania classic. If the creative team or management doesn't have faith in the angle to seel Mania-buys, that's on them... It's partly their job to build the story, and mostly the Superstars job to sell it.
It's actually sad that they don't have more faith in their own departments and talents. If they actually took the time to build intriguing angles, they wouldn't have to pray that two guys would get big enough on the Road to Mania to sell a match. There is no doubt in my mind that Cody and Goldust could have a real shot at stealing a show, if given enough time and resources to make it worth watching. It's not even difficult to book! I could probably put together an angle on my macbook in an hour that would convince lots of people to want to watch it!
In short, involved Dusty, put the title on the line against Goldust's career, and allow Cody to really cut loose in his promos. Make him really live the trauma of his childhood. Allow Goldy to really cut loose against Cody and Dusty from casting him away, causing the mental issues that would lead to his Goldust persona. Have Dusty try to play the peace maker, but in the final week before Mania have them brawl and accidentally knock their father down. Dusty is upset, he walks out on both of them, and tells them to settle their differences in a match that turns boys into men... a match he made famous: the Texas Bull Rope match.
See, how hard was that? I'd buy Mania for it if that's how it played out... In the end Dusty could turn on one of them. If he helps Cody they play the whole "I'm sorry, but your time is up son" angle in which Dusty basically retires his son and Cody gets the huge heel rub off it all. If Dusty saves Goldust it could be reconciliation for their family history, and is still a heel rub for Cody if he ends up beating them both down in the end.