Opti-Bond is a pro product that must be diluted to spray through a gun. So yeah it is cost effective. I feel less is wasted as well with this method If you want high gloss spray it on heavy. If you want a matte finish then spray one coat let dry and knock down with a sponge. The product stays on the tire for quite a long time. the high gloss shine will only last for a few days. this is dependent upon how much dust is collected on the tires while driving. I have also never had any problems with the tires browning out.
I have a few cars on weekly service and only apply the opti-bond every couple of weeks. I usualy clean the tires with the no rinse and a soft brush. The tires have a nice deep black look to them again.
As far as dilution goes For the wagner i use one third water to two thirds Opti-Bond.
If you use a compressor and a paint spray gun You can go one quarter water three quarters opti bond. You achualy use less with a compressor and the painters gun. It really atomizes the product well giving you a little more even coverage.
If you purchase some just play around with the dilution a little. Every one has their own preference on how things should look and work.