Funny then how they have a "tile improvement maintenace", it should just be "road maintenance" (or "road/railroad maintenance")
Inca's road UA is absolutely great. They don't pay for any roads on hills and pay for half cost everywhere else. Since you'll be settling on hilly terrain to take advantage of terraces, most if not all of your roads should be on hills. Every 2 roads that aren't on hills cost 1 gold, so you can basically free city connections. This is a big economic advantage that other civs don't get access to.
On top of that, it's also a military advantage. Roading your terrain like crazy helps immensely when defending, and paving a road towards an enemy city helps while on the offense. This road bonus does nothing but help them, regardless of what situation you are in.
The one thing I guess that would be good for, is if you needed to build a long road to a CS for a quest, and it wouldn't drain your treasury. Or if you built extra roads just for military's sake because you could afford it. Or if you had a sprawling empire (through conquest maybe) then that would be helpful. I guess I would be one to underestimate that UA since I hardly build roads, and rely on harbors for.
With that said, it still seems pretty shoddy though. But the hill movement is nice.
Also, haven't seen anyone mention it yet, but if Incans get the Commerce policy that reduces road maintenance, then ALL of their roads are FREE!!
No...
Can confirm Crus8r is correct, Wagon Trains' -50% road maintenance stacks additively with Inca's -50% road maintenance to give -100% road maintenance, ie. no road maintenance. This is because both Wagon Trains and Inca's road maintenance reduction work through the same variable, and since changes to said variable are always additive, two -50 modifiers result in a -100 modifier, not a -75 modifier.