Dunno about that. The new Battlestar Galactica had no characters that would have been even remotely likeable; the audience was rooting for the villains to let mankind out of its considerable misery and rid the universe of these disgusting worse-than-villains for good. Yet it was quite hooking...
There's little to like about a sympathetic character either at first sight ("They engineered him/her for the purpose! Too much syrup! I won't buy this!") or in the long run ("It's unrealistic for him/her to be so darn goodledy-good season after season! I want to see blood, tears and adultery!"), but a good villain is easy to despise regardless of the length of the exposure. Meaning the audience does care.
Letting the heroes take the back seat every now and then is good storytelling, too, at least beyond the 1950s standards. What good is a guest character if he/she is not allowed to meet the criteria of guest star
? Beyond season three, Trek lost its touch and started to treat the regulars as somehow inherently interesting - which is always a bad bet, and particularly so in a show that shies away from all conflict between the regulars.