I bought my N4 last November, so just a year old. I have it rooted and running xposed, gravity-box and a half dozen modules, plus some paid for "root" apps. It's running real nice, battery is as good as it will ever be, and if need be, I will just replace the battery from Amazon or some such place. I have no real reason to replace my phone as it does everything I need it to do, unless of course I drop it from a 12 story window.
As far as lollipop goes, I am in absolutely no hurry for it (I am an old linux user and learned long ago to let others do the all the early testing to root out all the bugs), so I could very likely keep 4.4.4 on this phone permanently.
However, I also have a bone stock N7 2013 that I will let upgrade to 5.0, so I can get to play with the new OS. If it really is that much better (and I'm not completely convinced that it is), then I may go to lollipop on the 4 and then root it after.