I use my leaf blower to dry my car too and if I'm not real quick I still get water spots. Unfortunately its a fact of life for some of us. I usually try and leave a little water on the car so when I do the final drying with my towel it gets wet and removes what water spots there are. You are very correct though- always try and wash a dark car out of the sun or in the shade or after the sun is out of the sky.
My son had a foam gun he got from auto geeks and while it does make putting the suds on easier it made no difference whatsoever in the amount of waterspots he got. Unless you have a fancy water purification system you are gonna get spots if you wash in the sun.