[Perfectlap]

I've clayed certain cars and saw very little difference. But those were very well maintained cars that were garage kept.

I clayed my friend's Corolla the other day. I don't think it had ever been clayed in 6 years. I washed the car twice and the drying towels were clean.
Then came out the clay and after one pass teh clay was filthy.
No need to mention that the owner of this car wasn't a detailing buff. Just the couple of visits to the car wash each month.

But even if you don't see a difference with the clay bar you should still do it before waxing. There are micro sediments that hook into the paint and clear coat.
The last thing you want to do is to roll that stuff around. Its like sandpapering your car.
In general I try to touch my paint as little as possible.
And when I do it touch dirty paint it has to be well lubricated with soapy water.
I don't believe in rinsing a dirty car with a spray gun either. You should remove the nozzle and tricle the water over the paint.