I would discourage you from commuting back and forth between Carlsbad and the zoo, Balboa Park, Sea World, etc. It would take probably an hour each way and if you get stuck on the I-5 in traffic, it will be much longer. Don't bother to spend extra money at Legoland to go through the aquarium...it's sad! Spend the money on Sea World instead. I second the Costco recommendation for attraction tickets...there is one close to Legoland that gets you a 3 month pass for less than the cost of 1 day - it also includes parking and the mini-golf.