I have single YamahaF 350. 1 year old, no issues so far. Run a Yamaha F8HT kicker.
Furthest I've been offshore is 20 miles, 3-15 miles is typical. Kicker can push me at 6 knots, a little more in perfect coditions. So I figure I'm no more than 3-4hours out if the main goes down. Though about going out for Tuna, but worried about trying to make it back from 50+ miles out in foul weater on the kicker (10 hours?).
I thnk, in general, I saved $$ and will continue to save $$ with the single (purchase, upkeep, fuel), but sacrificed going for Tuna with confidence. And I think Tuna will become more and more popular/accessable, although last year if I had twins that would probably have been only 1 or 2 trips.
If buying right now, I think I'd go twins, but maybe that's just the grass being greener...