Um.... given the strength (weak) of rebel attacks, any serious assault force (heck, even a mere raiding force!) would seriously out power any rebel forces. The only way they'd interfere is if you're trying for an AI style siege frigate raid
Actually, I've had rebels (multiple heavy cruisers and a dozen or so frigates) damage my force of a Marza (level 4) 2 siege frigs, half a dozen Cobalts, and half a dozen Javelis LRMS enough that I had to retreat. It helped that the rebels were attacking me instead of the Dunov (level 1) belonging to the person they were rebelling against! I know a serious attack force would have wiped both the rebels and the Dunov, but I didn't have one that wasn't busy at the time. Besides, why should I need a full-scale attack force to take down a planet that's had half of its orbital structures destroyed by rebels who theoretically support my cause and is currently being bombarded by those same rebels? If it had been just the enemy defense force, it would have been an overwhelming victory for me, but because 'my' rebels were there I was forced to retreat and come back later. As such a high-level tech, Insurrection should be more useful and less of an annoyance to the player using it. The rebels aren't enough to take a planet on their own, or to even threaten a planet with some decent defenses. They might be useful if they would fight alongside you, allowing you to do more with a smaller attack force, but for now they're only good for harrasing poorly defended planets that you don't have the spare forces to attack yourself, and then only if your opponent allows your culture to reach those planets unopposed!