Your data is still publicly available. You have to pay for Go Collect's data. It's always good to have multiple data points as well. I vote you keep doing it, and I'll keep watching! Either way, thanks for your service to the comic collectors over the years!
I have dabbled with the numbers myself to understand the dynamics of certain books, but I think they're right to utilize all their data in this way. The spec market is fueled by high grade chasing, but being able to track and weight across all grades shows more of a whole money view. I say you should still do your index too, for a while.
One thing I'm leery of is "averaging" sales. You can lose or obscure a lot of useful information if you average too much. Stock indexes use the latest values to provide a snapshot of the market. You could miss positive or negative momentum in the market if you average over a week or month.
