[Suicide Junkie]

Yeah, its way too easy to glass planets IMO.

However, capturing a planet is worthwhile...
Especially if you can identify the resupply depot / spaceport beforehand, and capture that to help your fleets keep rolling.
Plus you get the population for breathing other atmospheres, and a spaceport makes the recolonization productivity jump.

If you are against an enemy with racial techs, you could even capture a psychic training facility, or a religious shrine, and bask in its benefits.