I agree with Paul. I was also a highly trained athlete in college (water polo). We cross-trained running distance and stairs, lifted weights for strength and endurance. But the best swimmers and polo players were still the one's who had practiced the hardest in the pool.
That said, there's certainly nothing wrong with exercising in a variety of ways for a variety of purposes.
Personally, I find Aikido to be wholly sufficient in and of itself for the practice of Aikido. To further enjoy a healthy life I surf regularly and practice qigong daily.