If you're asking me, I would say to look at the true economic cost of a new phone.
First, PLEASE recycle your old phone! There are materials on the circuit board that can be recycled for new phones, otherwise they have to mine it from gorilla habitats in the Congo using child labor.
The little kids fit down the mine shafts better.
Secondly, given what we as consumers know about Apple's manufacturing, do you really want to support their business model? Can you look at your phone and feel proud about the manner in which your phone was made for you?
I suppose we don't know much about Samsung's manufacturing practices but Apple and Foxconn have been high-profiled in the international community lately.
I know my thoughts matter little here, as you've already said you want to upgrade "just because you can", and not because your phone no longer functions. But I will never support Apple products myself after the numerous offensive business decisions they have made.