Havng come from a striking art before doing aikido, and having also done other striking arts (both armed and unarmed) in between, there is certainly a good case for cross-training, if at least to learn how to attack properly.
I teach my students to really punch or cut thru, like they intend to really hit. None of this limp lettuce atemi waza stuff, I assure you! Besides, it's so much easier to apply waza when someone is really trying to knock your block off.
I think people are short-changing themselves if they're not putting an equal amount of effort into the atemi waza (when attacking), because from my point of view, it's the other side of the same coin.