1. A method, carried out on a waypoint server system, for incorporating a new waypoint, based upon a proposed place of interest (POI), into a current trip defined in a waypoint server system for a vehicle, the method comprising: configuring, on the waypoint server system, a trip definition for the current trip, the trip definition including: a current trip route to a destination, an estimated time of arrival (ETA) at the destination, a desired time of arrival at the destination, and a delay factor indicating a degree to which the ETA can exceed the desired time of arrival; determining, on the waypoint server system, a proposed POI for the trip definition based upon: the trip definition, and a collection of potential proposed POI instances; and issuing, by the waypoint server system through a mobile wireless network link to an in-vehicle user device, the proposed POI for presentation to a vehicle occupant; wherein during the determining, the waypoint server system processes the collection of potential proposed POI instances, to render the proposed POI, by: establishing POI ratings for individual ones of the collection of potential proposed POI instances, the POI rating for each individual POI of the collection of potential proposed POI instances being based at least in part upon: the delay factor, and an estimate of additional delay arising from adding the individual POI to the current trip route; and establishing a rank ordering of the individual ones of the collection of potential proposed POI instances based upon the POI ratings; and rendering the proposed POI from the rank ordering of the individual ones of the collection of potential proposed POI instances.