Our family has experienced the same thing. We used to go every October, and it was great. Quiet, relaxed, low crowds, with Halloween decorations. We'd ride everything, and spend alot of money shopping and eating in the parks. I remember days we went with a park hopper and managed to do all the rides once in a single day in both DL and DCA! Now that is no longer true, we've actually been on summer days that have been less crowded.
Our family has decided to give up on Halloween at Disney, except for the Halloween after hours parties on the weekdays. Those have been the only thing manageable for us crowd wise. And if we are only doing say, a single party a season instead of a multiple day trip like before, we are definately spending minimal cash on in park activities (like shopping and dining, not to mention hotel rooms).
Part of the problem I have is with the way Disney has been handling operations in what it considers "off season." We've gone on a October weekday, wall to wall people in the parks, only to see the rides run at half capacity (like only one side of Matterhorn open, etc), restaurants understaffed. It just makes me mad, and I feel bad for the cast members that tell us "its off season, we didn't expect it to be this crowded" because its clearly the fault of management if they can't call in back up. Really, a company starts seasonal events to increase business, and then fails to provide the proper staffing when the business actually increases? It just irritates me.