The great days of wrestling ended when ECW folded. Now, ECW was crazy and dangerous stuff, but they forced WCW and WWF to change, and I think for the better. But when ECW folded the Old ways started to crawl back in. Suddenly pile drivers are banned, and we're back to the "amazing elbows" and "suplexes" being the center point of Professional Wrestling. The day Professional Wrestling died for me is when Undertaker's streak ended. That was it. I was done. The end of the great era, which stayed too long and became sad and old. The Undertaker will always be my favorite wrestler, because his backstage real persona was one of kindness, service, and the realization that we, the fans, can see when it isn't being done to the fullest.
I've always been a WWF fan. However, there is no greater return than Sandman in ECW. Not because of the story, or even Sandman (I really really dislike the guy in and out of the ring). But because of the fans. Watch their reaction...that's what it was always about...the fans. (Mick understood that, Mark understood that, Shane understood that, the Dudleys understood, and so did Heyman. The rest...I think have forgotten.)
Vince and the WWE *need* competition in order to change. Like you said, ECW forced them to do that. When ECW folded, and Vince bought them out, he had a chance to save face with ECW fans, but Vince didn't want that. He wanted to do it his way, and he drove it into the ground. And, I agree with you on them ending the Streak, because it should've been one of the untouchable things in the business. Whether it was Mark's or Vince's decision, 22-0 would never be seen again. Now, at 21-1, it seems tainted, and just for the sake of "entertainment". Now Mark is a classy guy, and he wants to do what is right for business and the fans, so he could tell he was on his way out; but seeing him lose to Lesnar last year was still hard to fathom. Now that the Streak has been stopped, I really don't see a reason for him to come back at all. There's no real point...
And, IMO, one of the biggest returns was Triple H's, in Madison Square Garden, after his leg surgery a few years back.