When i've been in similar situations i've tried to look forward and not back. By that I mean, if it's getting a lot of downloads then let the people who have already downloaded it have it, don't change their experience by adding adverts in or damaging parts of the experience. Charge for new people to get the app. Saying that, I've never had it with as many people already downloaded the app, but i'd like to think i'd still do the same thing.
I have an app that I originally charged for and it got very little downloads, I made it free for a while and didn't pay much attention to the downloads, went back to it at a later time and noticed it had a lot of downloads so I started charging for it just to see what would happen, I expected to make it free again within a week due to no downloads. Downloads obviously dropped a bit, but still kept a pretty consistent level and have done ever since. I make a point of always improving the app though, so maybe that helps too but I just think it comes down to timing and having those previous downloads could help, it seemed to help me.
I'm not sure if you can turn a free Android app into a paid one though, I don't think you used to be able to, so that might all be pointless and you'd have to make a new id for it, but you've proved people definitely want it.
Whatever you do, good luck. I'm sure having a high downloaded app will help you at some point even if you don't manage to do as much as you want with this one. I hope you do.
When i've been in similar situations i've tried to look forward and not back. By that I mean, if it's getting a lot of downloads then let the people who have already downloaded it have it, don't change their experience by adding adverts in or damaging parts of the experience. Charge for new people to get the app. Saying that, I've never had it with as many people already downloaded the app, but i'd like to think i'd still do the same thing.
I have an app that I originally charged for and it got very little downloads, I made it free for a while and didn't pay much attention to the downloads, went back to it at a later time and noticed it had a lot of downloads so I started charging for it just to see what would happen, I expected to make it free again within a week due to no downloads. Downloads obviously dropped a bit, but still kept a pretty consistent level and have done ever since. I make a point of always improving the app though, so maybe that helps too but I just think it comes down to timing and having those previous downloads could help, it seemed to help me.
I'm not sure if you can turn a free Android app into a paid one though, I don't think you used to be able to, so that might all be pointless and you'd have to make a new id for it, but you've proved people definitely want it.
Whatever you do, good luck. I'm sure having a high downloaded app will help you at some point even if you don't manage to do as much as you want with this one. I hope you do.