I just don't think it's worth upgrading a phone year after year anymoreHow is that different from selling your phone? If I paid $800 for a phone last year and selling it for $400 today then I basically paid $400 to use that phone for a year.

In the first few years you had to worry about getting faster phones because the hardware was behind. The hardware is not behind anymore, LTE is standard on every carrier. Any flagship released in the past 2-3 years shouldn't feel sluggish, hell midrange phones are decent today.