That's the thing about sequels. You don't rehash and reference old material. You maintain the same style of humor and give new material. That's why I thought Anchorman 2 was very well done. The characters were all the same, everyone was the same, it just felt like a continuation of the first one, which is exactly what you want in a sequel.
If Anchorman 2 had them singing "afternoon delight" again, brick yelling "loud noises!" again, Ron saying his apartment smells of rich mahogany again, all to try to cash in on why those things were funny in the first one, it would have pissed me off. They did similar things to the first one (Brian's condom collection as opposed to the cologne collection, the news anchor fight, etc) but made them dramatically different. The first time Jim Carrey said "ah like it ah lot" in the first one it was funny because it was random. Pointing and laughing at someone's misfortune as opposed to helping them was random and funny. Doing the exact same jokes again takes out the random-ness, which essentially takes out the humor.