So... Why not just make all LRM-style units deal crap damage to structures? That way, in order to actually deal damage to enemy planets, you would need to make a sizable portion of your fleet -something else- so that you could effectively engage and destroy planets. It would also help after that first engagement, when you find out you're fighting a lame LRM-spammer, and inevitably suffer heavy losses... The retaliatory strike might strangle your fleet, but planet defenses could slow them down enough for you to rebuild and counter with some flak frigates or w/e.
To those of you who think LRM-spamming is not a problem:
I do not consider LRM's overpowered, or the practice of LRM-spamming to be an unbeatable uber strategy. I simply feel that fighting against an entire fleet of one unit type detracts from what is otherwise a beautifully complex and rich playing experience. The designers of this game obviously went through a lot of trouble to desgin specific strengths and weaknesses to each unit-type, and building craploads of LRMs sort of marginalizes the whole rest of the game. I know it's your pet strat and all, but fess up. You didn't buy this game because you thought it would be like every other RTS out there. We aren't playing this game to rush each others bases asap and get uber wins. We play this game instead of other RTSes because it's a slow paced, thoughtful, deep, complex game. LRM-spamming makes the game less complex, faster, and less strategic. So it's got to go.