Oz didn't hurt perception nearly as much as "Muppets From Space". Remember Oz was just a one-shot TV special. "Muppets From Space" was a theatrical release. People naturally expect more from a theatrical film than a TV special.
From a fan perspective though, Oz was no question the bottom of the barrel from a production standpoint in the post-Henson era. Oz also caused Disney to put Muppet TV projects on-hold for a number of years while they developed a strategy for what to do with the characters and their future. Releasing the first three seasons of The Muppet Show and launching a series of classic Muppet viral videos got the ball rolling in the right direction.
I have a feeling Oz is partially to blame in the huge missteps of the initial year of Disney's ownership. It got lukewarm reviews, the DVD's just didn't sell (compared to the actual Muppet Show DVD's)... the ratings were terrible given the fact they were opposite the prime time Emmy Awards and the fact that Star Wars episode III came out that weekend. It didn't capture the lightning in the bottle VMX captured to become a ratings hit (smashing a crappy Brady Bunch movie on Fox).
Oz was reportedly the product of a rushed production during the sale of the Muppets to the Walt Disney Company. The director really wanted to make a feature film so many of his aspirations fell flat and didn't get realized or fleshed-out the way they should have. A lot was scrapped and I think we got pieced-together remnants. There are some great moments in it and I liked Piggy's song. It just seemed like all the magic was taking place in the fringes of that movie rather than center stage where it should have been. Also, originally they tried to get Natalie Portman for the lead. That could have been an entirely different sort of picture. Probably a better one.
Rushed, and trying too hard to have that early 00's style adult humor that VMX pulled off almost flawlessly. Somehow watching it made me feel a lot more depressed and hopeless than Kermit's alternate time line in VMX... it's a lot drearier too. There are some alright concepts... making Piggy the villain wasn an experiment, but somehow it just didn't work right for me. If it was Muppet Babies, or an all Muppet production, yes... I LOVE what the writers of Muppet Snow White did. But it really seems that it detracted from the essence of the Muppets... other than MFS and Oz, Piggy and Kermit always shared some tender moment. Taking that out of a movie just feels empty. Of course, Oz, I'll forgive conceptually, MFS dropped the dang ball. I mean, epically dropped the dang ball.