[CONNECT .NET Addin] What is the proper method of getting the start & end point of an element?

The answer depends on what type of element and what you mean by "start" and "end" points.

I'd be happy with just a line element to get me started in the right direction. There is no lineelement.startpoint, and it is not in the propertygetter for the lineelement either.

Just at a loss on where to start.

Mike,
You will need to look into CurveVectors, CurvePathQuery
Example:
CurveVector curveVector = CurvePathQuery.ElementToCurveVector(element);

There is a lot of things you can do with the curve vector.