Charles,

that would be a nice feature really - but you can´t blow up a single planet (although you can blow up the entire system with a Terror Star - but it takes even more time than simply invading a planets, so...) but I see no reason why you simply ignore those small planets because, later on, try maxing out your influence and you´ll see those small planets flip on a constant basis - this saves you not only troops, but brings you new planets that are populated already.

Another way would be to select "rare" on planets before a game starts. btw, a PQ5 planet in ToA will become a decent planet after Terraforming etc & Weather Control....

To make the scenario end faster have the "Allow surrender" checked and change the stars to uncommon (but if you want to have lots of score with an military victory have it changed on occasional and the galaxy size large) on the galaxy setup. And also change the number of planets on solar system to abudant and planets quality should have the setup to abudant. Have 5 or 6 races for the scenario. This scenario should give you around 15000 to 21000 points if you win a military victory. I got around 15000 to 21000 points for this kind of scenario my self.

When you plan to conquer a opponets solar system try to take the planet with the highest number and when you have manage to do that don't invade the other planets around the recently conquered one. Instead try to win them by influencing them by building a cultural starbase. By this way you could save more of your own population.

Goodluck!