The eps I would choose to have made longer into a two part eps or more

When Richie almost dies. Part one: Richie would have still been unconcious. Fonzie would have had his little talk with God at the hospital
Part two: Richie would have come out of it and Fonzie would be by his side for the entire recovery.

HD 30th year reunion should have been longer. I hope it comes out on DVD with the next box set and shows more footage of the reunion.
I would have even settled for the entire softball game (minute by minute).

The Return of Pinky: Although there was never such an episode, it would have been nice since Pinky was so popular and commonly identified as part of the show even though she was only on a three part episode, it would have been nice if she would have returned.

The Break Up of Fonzie and Ashley: I wish this episode would have been made. I hate it when a series seems to skip an episode like this and then just gives a reason. It's almost like there was a bigger reason that the actresses for Ashley and Heather weren't on the show any longer.