I think that the feature that you are requesting is best accomplished in the OS, separate from OpenCPN. You basically want to synchronize your .gpx files between your computer and the Android device. You can currently do this by hooking up with a USB cable and using a sync utility in windows, but you would like to do it by Wifi instead. There are literally DOZENS of products that will do this for you. There isn't anything special about this - lots of people want to do this very thing with spreadsheets, text files, powerpoint, etc.
My advice is to keep OpenCPN simple and pick a synchronization tool that will do this for you. You might find that one of the cloud services is the best way to get this done. Then your computer and Android device can be many miles away from each other and you still accomplish it. Each would synchronize with your route directory in the cloud.
FWIW, I keep all my nav data (charts, routes, tracks, waypoints) on a microSD card, pull it out of my tablet and insert it in my PC. I run a Microsoft synctoy to synchronize the two, then put the microSD card back in the tablet. But that's just one way to do it. USB cable, Wifi, or cloud would all work
, probably even better. (I've been doing this for about 7 years, before cloud and AOCPN were widely available. I'm just locked into my old, obsolete way of doing it.)