Personally I get a new phone every year or so, I like to stay current with the best technology i can get when it comes to phones. There is always some cool new hardware feature that i want in the new version such as IR blaster, fingerprint scanner, better camera or whatever. Dont really care about OS upgrades to be honest, more often than not theyve caused my perfectly functioning phone to develop some sort of problem, sometimes major and sometimes just slightly annoying. Do these pure android nexus and motos phones ever have issues/bugs after an OS upgrade or are they flawless every time? I find it hard to believe they dont sometimes have issues as well.
Of course they can be a bit buggy, but I haven't seen anything catastrophic on the Nexuses I've used (including the 5 I have now); they've been worth any initial rough experiences. If your device maker consistently botches things so badly that you're actually afraid of getting their updates... it's time to change device makers. You shouldn't fear something that's supposed to make your phone more capable and secure.
Also, you're not exactly making a ringing endorsement for Samsung phones when you talk about your past devices (it's not clear if they're Samsung or not) sometimes becoming unusable after updates.
And yes, yearly hardware upgrades will 'solve' this problem, but you should never, ever have to do that just to get OS updates that work the way they're supposed to. That's excusing sub-par developers.