Just to summarise.
There will be one OBJ file (a single Poser prop) which will have one group per light (conveniently named to determine the type of light).
In the case of a Spotlight there will be another group (conveniently named) used to determine where the Spotlight will point at.

To determine the actual location of a light, the average position of the vertices in the relevant group seems the best choice.
To avoid having to do some math, I was thinking that creating a new Prop (would be invisible) for each target and then using the built-in PointAt for the Spot would be good (hopefully it won't cause problems even if there are a lot of lights).

I won't be attempting this before tomorrow (Friday) night.