OK - well all my apps are now running on 37 & despite the warnings in the console I haven't had to make any changes to E2E as the layouts still work fine. The only other changes I've had to make (apart from a few minor syntax updates for deprecations) are updating Play Billing to v9.x. There's also the new GMA Next-Gen SDK, which I've implemented in some of my apps, but at this stage it's not compulsory to migrate to it. All in all it hasn't been a major drama.
I don't have Bluetooth in any of them - but reading the documentation it seems that the changes are pretty minor & focus mainly around 2 new intents that it doesn't appear have to be implemented. There's pretty good documentation on how to add support for the predictive back gesture & if you don't have the time to do it now you can opt out & continue to use the existing behaviour.
I guess you have to decide whether it's worth investing some time in continuing to update your apps to be compatible with ongoing Android releases, but a lot of the changes can be copied & pasted once you've implemented them in one app. I decided a while back to unpublish about a dozen apps because the ROI wasn't there for the amount of time I was spending on updates on the total of 26 apps. Now I just concentrate on the ones that actually generate income & regularly review whether to retire the ones that aren't. I guess it's just part of publishing apps & I admit that sometimes it seems daunting, but generally it's not too bad.