The Ryan plan did hurt the republicans in the 2012 election because it made them look like they caved into the democrats wants and demands. It did not make the conservatives happy and so many of them stayed home and did not vote in the election. This let Obama be elected again.
No, I do not think that the new Ryan budget plan hurt the GOP in 2012, because Ryan was nothing but a boon for Romney's campaign. People responded positively to Ryan's budget. They appreciated all of the hard work that went into his budget, and he was a very agreeable person. He was not the reason for Romney's loss.
I think the Ryan Budget plan was a sensible plan full of conservative ideals while at the same time preserving the majority of programs that American citizens enjoy today, so while the plan may have been received negatively in the media for the amount of cuts it had in it I don't really think it hurt the GOP in 2012.
Most voters are not well informed about every specific issue; they vote based on broad strokes or large concepts. The Ryan budget plan was a major part of the GOP platform in 2012, but the vast majority of voters didn't know very much of what it contained; they only judged it based on the same broad strokes they used to judge the entire party.
Given that Paul Ryan is writing this years budget plan, I have to assume they aren't aware of the budget play for 2012 hurting them. I really think the problems with the GOP extend much further than their budget plan. I still can't figure out what they were thinking with Sarah Palin and then Mitt Romney.