Regarding different years
You asked about having a later ('76-77) model as a driver, specifically about it passing emissions in California.
Everyone seems to get their Underoos in a bunch with the "OH GOD, YOU'RE GOING TO HAVE TO GET IT SMOG TESTED!" argument, but really it's not a big deal if you're going to keep it fairly stock. Mine passes with flying colors every other year when I take it in, though it helps that the engine was rebuilt and doesn't burn oil or run strangely. If you do buy a later-year Bronco and plan to register it in California, be sure all the emissions plumbing is intact and functional, including the Thermactor pump and the stock air cleaner. (And obviously the catalytic converter, although as with any vehicle, you're allowed to do whatever kind of cat-back exhaust system suits your tastes.)
I've found that while the factory power rating of the 302 in '77 is kind of laughable (133 horsepower, although that was up from 1976's 125), the torque was rated at 236 lbs-ft @ 1800 rpm, and for these vehicles torque is really your friend. Even having a Ranger with the added weight of a roll bar and air conditioning, I don't really find mine to be underpowered when entering freeways and what have you. Is it a muscle car? Not by a long shot.
As a driver, the big advantage to the '76-77 design is the power disc brakes and the revised steering set-up. The latter doesn't suit everyone, as it's great for an unlifted street-driven Bronco, but less desirable for one with much of a lift that'll do some serious crawling. Obviously disc brakes can be added to the earlier year Broncos.
Finally, to address fuel economy, how you drive and how it's set up will make a big difference. I find that out on the road, if I go 65-70 I get about 12 miles per gallon. But if I can hold it to about 60, the mileage goes way up to about 16-17. The Bronco's aerodynamics (or lack thereof) really come into play at higher speeds. Huge tires will also diminish gas mileage to a degree. Around town I see about 10-12 mpg.
Just a little extra info for you!