My experiment about the effectiveness of CTR vs Impressions was made solely on AdMob and I already got some apps on there with low Impressions and no refresh at all.

So, as far as I can tell, there are some conclusions about it - even now, where the experiment was running for many days but not months.

Generally, yes, you will get assigned higher CPC ads, when your CTR is high. These CPC goes up to nearly 10ct per click which is a really big number for admob (regulary average is around 2-3ct/click).

So yes, in combination with a high CTR you will be able to more than double your revenue - that's my calculation about it.

BUT - and that's a big problem - at least admob does not have much high CPC ads in their inventory or not enough to feed a popular app with. So if you get very small impression count, you may get better revenue when your CTR is high, because there are some high CPC ads available which will be assigned to you.

For a higher Impression Count - unfortunately you will not get always that much high CPC - because there are simply not enough in the inventory.

It may be possible, that this is a generell problem with ad networks as long as you do not have control over your minimum accepted CPC - you cannot control it in admob for example.

Also AdMob does not allow you on their website to offer a lower refreshing rate than 120sec.
Also AdMob does tell on their frontpage how many Ads they delivered! (not clicks)

So that let me think, that admob does not aim for high CTR but for a high Impression Count and so their inventories will drain fast and leave you with a regular average CPC of 0.03$. sometimes more, sometimes less.

Beside that fact you still have to care for different countries with different CPCs out there, so your userbase is another factor which you have to mention.

If a game get's very popular in countries where the CPC is generelly lower (because lesser advertisers are around there) you may also get lower revenue and it could pay off better, when raising the Impression Rate again and do some house ads - or even maybe do advertise your own paid products.

So that is my conclusion for this time - it would be also interesting, when supporting admob with another network trough mediation. But because I would need to update the sdk and therefore my apps and integrate all the different SDKs as well - I just didn't tried, instead I would be more comfortable with implementing MoPub directly, which is less work for me :-)