The shortest and thus most logical way of getting to Mexico City and back, from Hilo, is:
Hilo > Honolulu > Los Angeles > Mexico City > Los Angeles > Honolulu > Hilo
That's 216 + 2553 + 1552 = 4,321 miles each way, or 8,642 round-trip. Since there's a 500 mile minimum per flight for frequent flyer miles, it'd actually be worth 9,210 frequent flyer miles, if I did it all on airlines that I earn miles on.
But... I found a decent price (on airlines I earn miles on) for:
Hilo > Honolulu > San Francisco > Atlanta > Mexico City > Detroit > Cincinnati > Honolulu > Hilo
That's 12,776 miles round-trip... and worth 13,614 frequent flyer miles. And it's pretty similar price-wise to what I was finding for shorter routings.
So, hmmm. Do I choose to spend a lot more time on airplanes, but not necessarily any more money? :)