I find the responses here really quite predictable. Those who are good at atemi or want to be good at atemi say that punches should be more than just a setup for a technique, they should be a technique in themselves. Those who are not good at it (or don't wan't to be), of course say otherwise.
Imagine having this debate in a karate forum: "Should punches be strong?". kinda funny isn't it?
I think you're missing the point that aikido makes the bodys movement strong and this makes the ukemi strong/effective. Actual "punching" practice is of no interest to me and has less practical aikido application than practiscing any technique.