well for me personally, i was in the camp that didn't care about size. by that i mean i didn't NEED a larger phone for anything. i have been using the ip4 on verizon since it came out 3.5 years ago. i watched tv shows and movies on it 2x a day while taking the train to work for nearly 2 years. i browse the web on it and i have used google maps and all the apps no problem with it. i definitely liked the compact size of it though when putting it in my pocket or in a book bag or something.
so it wasn't that i necessarily said the size was perfect, it was that it was good enough for me and i didn't "need" anything bigger. and pretty much anyone who ever told me that my phone was too small and i needed a bigger screen, i simply asked them "why?" and to that, they had absolutely no response other than "because its bigger, blah blah blah". they couldn't give me one reason why me personally would NEED a bigger screen.
now with the ip6, i opted to get the ip6+ for a couple reasons. the main reason was because i wanted to see if a big phone would be okay to me and if i would like how large it is. if i didn't like it, i could downsize to the ip6 and then i know that the ip6+ is too large for me. had i gone with the ip6 first, i would be wondering if i would have been happier with the ip6+.
2nd reason is the specs on it over the ip6. the battery is better, has a slightly better resolution (which to be honest i don't care about personally), the camera is better and with my first kid on the way, i'm thinking i will be using my phone for a lot more pics/vids than i did in the past.
3rd reason was because my wife is getting the ip6 next month. i develop apps on the side, and it will be nice to have 2 physical devices to test out my stuff on. the simulator with the ios SDK is pretty awesome and works great (million times better than android emulator, but that is for another thread) but using the physical phone is simply easier to test stuff than with a touchpad on my laptop.
but regardless, i was going to upgrade, because im on a phone that is 4 years old and i'm on ios6, and things are starting to slow to a crawl on it. and i also NEED to upgrade to ios7 for some of the apps i use, including the one that controls my home theater, and no way i was putting ios7 on my ip4 for performance reasons.
i just opened it and it honestly doesn't feel as big as i expected. i haven't turned it on yet, waiting to set it up after this roger goodel press conference. but i think part of the reason it doesn't feel as big is because it's pretty thin. in the case i got for it, it's thinner than my ip4 is without a case on it.