This is an interesting question because I think it really depends on who's perspective is being taken, and on the important factor of overall game condition, which will dictate the actual resale value. The local area supply and demand factor for each game should also be considered.
As for the individual perspectives:
- You: Do you really desire a SS more than the TAF? If so, then why? Did you just get tired of it, or did you onquer iit and didn't put much time on it? Why keep it if you don't play it. Will you miss it after its gone? If your TAF is in really good condition with no mansion insert wear, and excellent playfield condition, then consider your game closer to the $6K price range.
- SS owner: Same question as above except substitute TAF/SS.