I work for a small game studio that develops games for iOS and Android currently. The engine we are building will be portable and our upcoming game is quite ambitious. Therefore we are considering porting it to PSP also, making it available at the PSN as a mini. I have been searching for days now but I am having trouble finding any numbers of what an average PSN mini game can sell. What a hit or a bad game could sell is also really interesting. As we are trying to calculate if it is worth going into this market any clue would be helpful!
If you're seriously considering this I'd speak to Sony directly. Sales numbers are usually considered commercially sensitive, not only between competing game developers/publishers but between different platform holders. As a developer Sony would probably be prepared to provide you with generalisations on some of the numbers for what you could reasonably expect.