This web site is just cranking up.
It's a subcription service but you can sign up for a free 14 day trial.

SmartCollector

You can research how certain catagories do on ebay over the years. In the "Trend it" section, I input Spawn. Interesting results.

Spawn ebay info

Whoops! I guess you have to be signed up to see that info. Ah well...it is 14 days free.

I haven't determined if any of it's useful or not.