Most people seem to have the impression that higher water temperatures help to set the stage for achieving wen growth. In actuality I have found it is the lower water temperatures which seem to yield the most changes to wen growth. Also from my research some have said their goldfish get the biggest wen growth in low temperatures around 54F, but I have found you can start getting wen growth results just from reducing your water temperature to 71F.
From most of the research I have done a lot of people seem to feel certain foods (or brands of goldfish foods) will yield amazing wen growth results, and even goldfish companies try to promote their foods making them sound as if they are geared toward wen growth, etc. A fish with a healthy diet should thrive in general but in terms of wen growth I found wen growth may be more geared to the amount of food it's being fed rather than what you're feeding it. Now if you're feeding your fish a lot it's basically going to grow bigger at a more rapid rate, but this is more related to its body size and not its wen growth. I found feeding a goldfish less may allow the fishes body to not grow as fast at a more rapid rate and instead the nutrients of the food may actually go to contributing to the fishes wen growth. This may be another reason why one would see more rapid wen growth in colder temperatures as well because colder temperatures make goldfish slow down their activity level and they ultimately begin to eat less. So if you want your goldfish to have good body and wen growth, try using a quality goldfish food and finding/calculating the right amount to feed them while keeping the temperature and their activity levels in mind.
A lot of goldfish may seem to never achieve much (if any) wen growth and I find this could be more related to the fish's genetics and probably poor breeding standards to some extent. If you buy a small young colored up goldfish and it looks as if it really has no wen growth coming in currently than don't expect as your goldfish grows up that it will achieve any, because I have found more often than not it just won't really. If you want a goldfish with big wen growth, I would suggest looking for a goldfish that currently has some good wen growth coming in before you decide to raise that fish thinking that it will achieve wen growth as it grows.
If you have a fish suffering from things like Swim Bladder Disease or some underlying issue (again certain problems could relate back to genetics/breeding), this could possibly be a reason why you aren't seeing any significant wen growth happening (although an excess amount of wen growth could actually become problematic for goldfish as well). Again, this can relate back to also providing the fish with a healthy diet. Another part of a fish's health is having a clean habitat, most serious goldfish keepers tend to do rather large water changes, either doing them daily or weekly is what seems to be the norm. If you aren't sure when to do your water changes at least test your aquarium water weekly and see what your water stats are, in doing this it can help give you the knowledge you need to keep your aquarium healthy and provide your goldfish with the best habitat for achieving things like wen growth.