A lot of different things converging here…
First, ST has never, to my knowledge, advertised microlocation uses for their presence sensor (like knowing who’s in the bedroom). It’s for crossing a geofence boundary. So I’m not sure the lights in the bedroom example applies.
But as far as stabilizing it in general, this works quite well:
As far as tolerating random lights coming on…with the exception of things triggered by presence detection, I’ve never had a problem with things randomly coming on. I have had multiple issues with things randomly not working, as have many people. So I always have a plan B option for anything run by ST.
ST solved some important convenience use cases for me and I’m happy with that. In particular, I have decent voice control and an IFTTT channel, both high value features for me.
If you want a home automation system under $3,000 that has always made stability and reliability their top priority, look at Staples Connect. Their Target market is small businesses, so reliability was their big issue from the beginning. They got there by avoiding cloud services, not using Geopresence, not having an IFTTT channel, not allowing user-developed code, and offering a much more limited selection of generally more expensive individual devices. Basically they threw out anything that might cause instability. If you look at their forums, you’ll see that most of the complaints are about devices that they are not supporting yet. Not about instability in the system that people already have.
SmartThings chose to offer a much more open platform and chase a lot of the hottest, newest stuff, even if they didn’t offer full integration to begin with. That comes with a different set of issues.
It may well be that ST isn’t the right fit for you. My personal guess (just a guess) is that by summer 2016 we’ll see several reliable plug and play home automation systems. Apple Homekit/insteon will be one. I fully expect Samsung/SmartThings to be another. So I’m putting off my big HA projects until late 2016.
For now, ST fits my interim needs best. I like the vision, I like the community, but I’d jump ship in a heartbeat if a competitor had a solution that was a better fit for what I need right now. But for right now, ST is solving some things I want solved. Your value calculation may be different.