Rarely, but not never.

But, that's probably because making a hit is very hard. The shows that are considered for a reboot are the hits. So, not only does it have to be a hit, but it has to be a bigger hit than the original.

That's probably why the good remakes are remakes of something that was a hit because it broke new ground in some way, rather than just having great acting, directing, writing, etc.

The original Star Trek was a hit not because the writing, acting and directing were top notch, but because the show had female officers, it had a Russian helmsman working with American officers. It had TV's first interracial kiss. It aired during the cold war, but depicted a post-capitalist world that might arguably have been communist. All that mattered more than the writing and acting. When they rebooted it, they could get great writers, directors and actors. Same general idea with Battlestar: Galactica and Doctor Who.

This also explains why it would be hard to reboot a sitcom. Sitcom situations are... um... common. Typically sitcoms don't break any new ground. If they're popular it's because of good writing, acting and directing. This might also be why some people thought the Will & Grace reboot was good. The first one was popular partially because it broke new ground, depicting homosexuality in a positive and normal light. Arguably that mattered more than the acting, writing and direction.