Android - Advanced searching in Play app store?

I created this.

It's an advanced Google Play search engine, I wanted to create that a long time ago. Now, it's done

Since Google doesn't have an API for Play search, I use an open source scraper.

Almost all app specs can be filtered and sorted.

I hope you'll like it, and please let me know if you find any bug or have any feature request.

It's open source : KPlaysearch

I also created a similar application (http://play.gqqnbig.me/) to KaKi87's. Source code is at https://github.com/gqqnbig/advanced-play-search

Looks like what the OP is looking for can be done at AppBrain, using the &sort=popular URL parameter. See e.g. this example search for file sync: First result page mosly holds apps with 10k+ downloads with a good "internal rating" (they have their own "rating number" in addition to the playstore rating). Checking some, they seem to have 10k+ ratings on GPlay as well. Additional filtering is possible for free/paid, new/updated, app2sd, reduced price.

Though not being exactly what was asked for, I guess it's pretty close. Another good result list can be obtained with the &sort=highest-rated variant, which seems to sort by playstore rating: "file sync" by rating.