I have saved seeds from wave petunias for several years. Waves are called a F1 hybrid. The following generation is F2 and so on. Generally most of the F2 generation are quite close to the original waves, although there can be some very nice color variations as well as some that will flower stripped. The F3 generation onward seems to loose more and more of the wave characteristics as well as a loss of vigor.

For me, what has worked the best is to always have a planter of true Waves (F1 generation). So I will buy or plant from purchased seeds 6 or so waves each year. Then I collect the seeds from those plants and grow a large number of F2 plants each year that I use to fill in mass planting and the majority of my planters. I really like the variety I get from my F2 plants. Anymore, I don't plant any F3 and up generations.