I have owned two smartphones so far:
- A Samsung Intercept, which was a low-end (even at the time) Android 2.2 phone that happened to be the very first smartphone ever offered with a non-exhorbitantly-priced service plan in the US (from Virgin Mobile).
- A Nexus 5, which I would call "highest-end" even though it's half the price of an iPhone 5s or Samsung Galaxy S5 (both of which are rip-offs IMO), which I use with a cheap T-Mobile almost-data-only plan and VoIP
The Intercept had a physical keyboard, removable battery and removable SD card, all of which are features I valued. It was also better at making phone calls -- the speaker on the Nexus 5 is a bit weak. However, there's no way in Hell I would switch back to the Intercept because the user experience is so much better with the higher-resolution screen and better CPU/RAM. Even just navigating around the operating system interface is better, let alone performance of actual apps.
Today I was playing Bioshock, one of the top games on the Xbox 360 released just about 7 years ago...on my phone. It was certainly an "I'm blown away right now" moment. And you know what? I can buy a used iPhone which supports that game, for between $200 and $250.
I agree with the idea that you definitely start hitting diminishing returns once price gets above that range.
I was watching Star Trek on Netflix on my Nexus 5 the other day, saw one of the characters carrying a stack of PADDs around, realized that my phone was more capable than said PADDs, and thought to myself "wow, I'm living in the future!"
If I were in the market for a cellphone today -- and I might be soon, since my wife's Samsung Captivate (AKA original Galaxy S) is starting to fail -- I would be strongly considering the Moto G (as well as the Moto E, Moto X, and Nexus 5). I'll probably hold off on the decision at least until the next Nexus comes out, though.