Something you must keep in mind is that our choices in term of UCs (and most particularly unique units, because of the 3d models required) are limited by the ressources we have at our disposition. The chasqui model and icon are particularly good and have been used thanks to the authorization of JTitan and Leugi. This, plus the fact that there is almost no incan civ mod, means that, except for a surprise, we'll have to keep this unit for the UC.
That said, modifying the bonus of the unit can indeed still be discussed, even more when it happens that pineappledan just added a new bonus to the unit through a Sailing->Writing tech displacement. The chasqui is in a bizarre spot right now : it must be one of the units that has known the must changes, but it still appears a bit bland. Its purpose as a unit is supposed to be that of a inland scout that can later serve a defensive purpose : with its bonus, it can quickly reposition and defend secondary shockpoints. That said, I agree that it is not really satisfying, and its role can be fulfilled by other units quite easily...
My idea is to keep the identity of the unit as a communication-focused scout (being messengers, chasqui aren't really meant to be a militant unit), so no additionnal combat bonus, but make it a sort of all-purpose unit.
For that, giving it the ability to build/remove roads seems indeed a good beginning : in times of peace, it shows how chasqui are a crucial part of the Incan communication system (workers will be working enough on putting terrace farms everywhere in the early classical era) ; in times of war, having units with high defense (through survivalism promotions) and capable of creating highways for troops seems good enough (plus it synergizes with the monopoly bonus given by the unique Incan granary).
For the other bonus, we should discuss a bit more : a medic bonus seems logical enough at first sight, but this has several problems. First, it overlaps with the other healing sources the unit has (unique promotion + survivalism). Second, it would mean putting the unit in the backline for most of the fight because of the defense malus this kind of promotion gives (which would contradict its other bonus). Do you have ideas on that matter,
@pineappledan,
@adan_eslavo ?