Except food is freely available from CSes, making it the least important yield to worry about in most cases.
But not nearly as easily now, at least for non-capital cities. Are maritimes even the best use of gold now? I honestly have no idea. In any case, extra food never hurts!
Anyway I've just been playing an Inca game and I really quite like them.
The civ trait is actually pretty great (considerably better than Hiawatha's, I think) - I was always a fan of Brennus in Civ IV and this is his hills bonus on crack. The extra mobility is just great in a whole range of situations, both in getting to a fight and getting away from a fight. It also helps out early scouting and thus your chances of more ruins.
The slingers perhaps benefit the most from it; they can move to a hill and fire in the same turn, and they can more easily escape and harry a pursuing melee unit. Their actual ability is nothing special, but it gels well with this; it cuts down on the need for screening units and lets you operate them as skirmishers rather than necessarily as part of a formation, and it lets you risk bringing them a little further forward. They're also really good against barbarians.
Cheap roads mean trade routes really pay off, and even better mobility since you don't have to be so picky about where you build them.
And it's hard to quantitate, but the increased mobility of workers also probably adds up to some quite significant turn advantage too.
So yeah it's actually a pretty massive efficiency bonus, and not just tuned to warmongers.
As for terrace farms, yeah they're situational but I like them. With one mountain they're like a post-civil-service riverside hill farm (without the gold admittedly), so more of those on tiles away from rivers is pretty sweet. With two or more, they're like a resource special. For a civ that is designed for large empires, it's great for letting you settle land that the others don't want. Especially for making ludicrous production cities in the hills where the lack of water might choke another civ.
Also with all the other hill stuff it means the Incas are basically dwarves, so you can give all your cities names like Boatmurdered and Oilfurnace and have cool dwarves-vs-elves battles with Hiawatha and so on.