[chulipuli]

Ignoring them: nothing happens.

Answering them: Could net some love from the market.

I would create a template message explaining why you did not answer (be honest), why you are answering now, and asking if they continue to use the app so that you can support it properly.

It won't hurt because most people won't care. Those that do will most likely appreciate it.

Still, how much is your time worth?