Are the following Skaven Champions worth the points? If so, why?

Basic clanrat = 4 pts. The champion is +8 pts, which only has +1 attack (WS3, S3).

Nightrunner = 7 pts. The champion is +8 pts, which gets you +1 BS, and a 6+ ward save. Nightrunners have no armour save.

These last two units are typically small (5-10 models):

Plague Censor Bearers are 16 pts (which have 2 attacks and +1 for frenzy). The champion is +13 pts, which gets you another attack. Am I not better off just buying another PCB?

Jezzails are 20 pts. A champion is +10 pts, which adds +1 BS. Am I not better off just buying another jezzail?

Thank you for any insight.