Just wanted to add an update following some experimenting I did recently:
I have two RPI3's purchased at different times and running the version of Raspbian that was current at the time so one has Jessie and one has been upgraded from Jessie to Stretch. Both get apt-get dist-upgrade every so often and were updated for this test. They both run 24/7 without reboots and connect via wifi, I use a bluetooth keyboard to interact with them sometimes (SSH other times)
The older RPI3 has always had rock solid reliability for WiFi, the newer one has always dropped the WiFi connection and not automatically re-connected (or thinks it is connected but passes no data) at random intervals but usually a couple weeks apart. If the WiFi has been dropped then the bluetooth keyboard will also fail to connect, a reboot always fixes it nothing else seems to.
As an experiment I swapped the SD cards around to see (unscientifically) if there was a problem with the raspbian image on the troublesome Pi, or if it was hardware related. Both Pi's proceeded to work faultlessly for weeks (way beyond when an error would have occured). Then swapping the cards back to their original Pi's both have still continued to work faultlessly without dropped WiFi or unresponsive bluetooth. No changes to the wireless network configuration were made during this time.
I am not technical enough to understand the significance of these findings, but thought someone else might. The only thought I had was that the troublesome Pi didn't get or successfully apply the firmware update for the wireless chip released a while ago and swapping the cards around made that happen.
One (unreleated) thing I have noticed is that my older Kindle Fire which has bluetooth and wifi also has all the same problems with WiFi dropping out regularly when a bluetooth speaker is connected, but works fine if the bluetooth is disconnected. No idea if it shares any firmware hardware or driver similarities with the Pi, but clearly there is some lingering bugs in various implementations of bluetooth and WiFi combined chips. The newest kindle fire (different hardware) works fine.
I am happi-er as the annoying problem of wifi dropping out has been fixed for me, thought I would post the experience in-case it helped anyone else out or gave anyone chasing bugs some ideas. The bluetooth still remains a bit flaky, and I wouldn't really trust it for a keyboard/mouse solution in any environment where the Pi is going to be "installed" inside something permanent or given to non-techy users. One with a wire or its own non-bluetooth wireless adapter seems like a better bet.
Happy Raspberry-pi-ing and thanks to the Foundation for all the great work they have done getting the Pi platform as well supported fully featured and reliable as it is (I have Pi's running very reliably for years now, including some Pi3's maxed out on BOINC tasks all the time, without any human intervention required, which to me makes a very stable hardware/software combo).