$4k? That's about 3.5x more than what I pay yearly.
Yeah I spend $700-$800 a year and I have an S4. I keep a phone for 2 years at a time, previous phone was an S2. The changes one version to the next are too incremental to notice, but after a couple of years I notice a phone tends to start annoying me.
To people complaining about a smartphone killing your productivity, you just have to treat it appropriately. My phone stays on silent face down on my desk most of the day. I don't give my mobile number out to clients, either.
I get most productive uses out of it when I'm travelling. Long train/car journeys, when out of the country, etc.