We went two years ago when our son was 6 and it was great. He loved it and we all had a good time! We read somewhere to walk directly to the back of the park and then work your way front, as that will help avoid the crowds. We did that, and it was awesome. I don't think we waited in line longer than 10 minutes and it was the middle of July. We stayed one day and felt like we saw everything. We didn't stay at the hotel - just drove there and back from Disney. I'm sure staying at the hotel one night would have been fun too, though!
At the time, the monthly lego magazine that you can get at lego stores had a buy one get one free coupon every month to legoland. I'm not sure if they still do, but it's worth tracking down.