Back in the day when fading stars needed a place to go, they went en masse to Love Boat and Fantasy Island to regain some of their popularity and to earn a few quick bucks. If you wanted to be on the show you knew that you were going to have share screen time with other fading stars and if you didn't want to, then you would not be asked back.
Apparently Alicia Silverstone thinks she is some kind of megastar. She was due to make a guest appearance on How I Met Your Mother, but when hearing that Britney Spears was making a cameo on the same episode, she pulled out.
Alicia thought it would be "chaotic." I think it is because she wants to be the center of attention because it happens so rarely now. Every couple of years some network will throw the dice and take a chance on her for a series which eventually dies an early death in the ratings. The only other time we ever see her is when someone trots out fat pictures of her, and then the inevitable, I lost 20 pounds article.
What Alicia should have realized is that the episode she could have guest starred on is going to be highly rated. Not Super Bowl or American Idol ratings, but higher than any of her disaster television shows have ever got. People would have said, "hey there is the chick from Clueless. They should put her in something again." Instead, Sarah Chalke from Scrubs jumped at the chance when Alicia said no.
I like Sarah Chalke better anyway.