Try and keep in mind that the more freely available extensions are the faster the community will increase. If there are loads of extensions around no one knows about it's a shame.
Or maybe one could add them to a list of 'paid' extensions (official, unofficial, paid).
That way people wanting a certain extension can see easily if there's something similiar around.
Also; if I've paid 200€/$/£ for dev of extension XYZ, if that dev sells a nearly unchanged version of it for 100 - shouldn't my price go down or I be compensated to a certain extent? That would ensure people who have the idea for the extension but can't do it themselves also have an incentive for helping grow extension use....
I think you should keep track of what is being sold/made Utchin. It's not in the interest of community otherwise. There's a way to get ext devs paid and give people buying specific ones a fair deal. http://www.ugg2u.net
But I guess that's incompatible with GPL licence (selling certain extensions over and over?)