We can absolutely recalibrate a C3.
It just cost more than a new C3. Speaking to the costs of service, I wonder what the actual price of a spyder re-calibration is, because I've never heard of datacolor offering that before. If you want a meter that is actualy is more stable over time, then a i1 Display Pro is a better choice than any meter that has exposed filters.
As to they way our software works, it doesn't fixate on the controls your TV has. It gathers the data and shows you what the issues are. We offer guidance on which controls affect the data you're looking at.
Honestly if you only have contrast, brightness, color and tint, a meter isn't going to help you setup your TV much more than a disc will. Calibration with a meter really starts when you start adjusting the White balance controls and if you don't have access to those adding a meter to a calibration disc might help you change tint or color by a click or two, but it won't have the drastic impact that adjusting grayscale can provide.