Mentioning a stand alone episode of Angel as being reason to cancel Angel is like saying the Star Wars Christmas Special was reason to cancel Star Wars. The stand alone episodes have almost nothing to do with the series. They're just there. Most series have twenty-four stories per season (or so), but Angel and Buffy tend toward having one story. If any other show has one bad story, people just wonder what's on next week. If Angel has one bad story (which unfortunately equals an entire season), everyone wonders when it will be cancelled. A stand alone Angel episode is analagous to a couple of minutes of standard dramatic fare; it's a break from the story where a small little scene would happen in another show. I can't make the case that a show needs to be cancelled because of a couple of minutes.
Just really quickly though: You said, "Sorry, but if you have to resort to turning your main [character?] into a muppet just to attract more viewers." I would wonder how this could be construed as a ratings grab. Do muppets tend to pull major ratings among target demographics?
As for the Dracula episode of Buffy. I can totally see why that was largely played for laughs. When I first heard Buffy was going to meet Dracula, I started laughing almost immediately. With Dracula's being a completely fictional product of Bram Stoker's misunderstanding of various Romanian historical figures and generally confused portrayal of vampire mythos, it would be like writing a movie about astronauts going to Mars and meeting Star Trek's Mr. Spock! Try to be serious and fail; play it for laughs and it's great.
Don't get me wrong, it's awesome that you like the series, and I'd love to hear some of your thoughts on the positives of both series, but to me the muppet episode was a non-event. It was a poke at Barney and how long our little sister/brother/cousin/neighbor sits transfixed in front of the screen watching what we all know has to be some nefarious byproduct of Satan wrapped in fluffy packaging. From what I understand anyway, David Boreanaz was unable to film (because he hurt himself if I recall) so they threw together an episode that didn't require him to be on set as much.