The biggest difference you will see in going with a lighter wheelset is quicker acceleration and easier climbing. Like some others have said, new wheels can make a world of difference. It's neat that you can actually feel or sense the bike "lurching forward" when you accelerate. They can make a huge difference when you're trying to close a gap or bridge up to a group. If it were me, I'd make the bigger jump to a 1400-1500 grams (1600 grams tops) wheelset. While it's probably a lot of wheels for your current frame, you can always just move them over to the next bike. That is what I do. And with your weight I wouldn't worry about the higher spoked wheels. I ride the lower spoke count wheels and am 25 lbs heavier than you and have never really had an issue. You should be able to get some huge discounts on '08's or '09's.