The early 90's were worth it in my opinion. Those teams were awesome and a remarkable pleasure to watch. Heck, Harper's catch against the 49ers ... E. Smith's separated shoulder game ... and so many other memorable games. Those games and times were wonderful.
Also, I enjoyed almost all of the Parcell's tenure in Dallas. Son of Bum's first regular season was very good. The second half of the 2009(?) season when the Cowboys beat the Eagles two games in a row ... that was pretty nice.
More recent seasons have been mind-numbingly bad, of course. And the near future isn't even remotely promising. But those early years were so good that I'd keep them, even if it means that today's futility has basically turned me into a non-fan, free agent now.