First let me say that unhealthy plants that do not receive enough water and nutrients may be subpar in performance in all the categories mentioned. Discolored foliage, oddly shaped or very thin blooms etc.
Can't comment on the seedlings yet, they are too young here. But I suspect they will improve in a few things and be very much like the more mature plants and stay pretty much the same in other areas.
As far as water and fertilizer are concerned (I think these work together) how fast the plants multiply definitely seem to be increased by having sufficient amounts of both. I think we all know that the roots and foliage (obvious from some of the pictures posted of plants received from some hybridizers, but also evidenced in my own garden) are very much increased by fertilizers and sufficient water. I think as a result and assuming enough sun is given to the plants, then the branching and the bud count will improve and even the size of the blooms.
I can't say that the height of the scapes actually improves with water and fertilizer, (I have not been able to say for certain that is the case in my garden), some plants might benefit from taller scapes, but for sure some never seem to get taller.
The color of the foliage can definitely change with the addition of some fertilizers and the color of the blooms I think can actually change with the addition of fertilizer.
I personally have not noticed any change in petal substance, colorfastness etc.
