I don't think it would even take a 5th gate, just some new attractions. And to be fair they are working on it, however slowly. A big part of the problem right now is that only one park is really worth a full day for most families, while the other parks lack enough attractions to disperse the crowds. Just in the past week I've seen reports of 200 minute waits at Tower of Terror because Rock N Roller Coaster was down, heard Epcot described as "shopping and dining with a hundred dollar cover charge", and read the advice that Animal Kingdom can be done in 3-4 hours. Is it any wonder that wait times are an issue when Studios has only 5 rides and several of Epcot's pavilions are aging and/or standing empty?
I do still enjoy Disney, but we've reached the point where paying more to get less is no longer something we're willing to swallow. I'm glad we had our "Disney phase" when the kids were younger, but now they're getting older there are more alternatives competing for our vacation time and money and Disney just doesn't measure up to other experiences any more. We used to go just because it was where we wanted to go; now we go for specific/special events and take our big family vacations elsewhere.