We've seen it before, and I'm afraid it will happen in the future... many interesting MSX groups like Bandwagon, Mark Jelsma and TeddyWareZ stopped creating new products for MSX as there were low/no sales and mostly only negative feedback.
We have got some ideas up our sleeves that might improve the sales and feedback part on the long run, but I think it's good to discuss what we can do about it now. For starters... buy new software, don't copy. It destroyed too much already.
The second part is not as easy... personally I think developers should be aware that people only contact developers when they are not satisfied, when they have questions. Most people never contact people to say 'hey your software is great!!!'. So getting no/little feedback is actually a good thing. Just as long as your sales/downloads are doing fine