I recommend it. I was in the same boat. Bought my iPhone 4 with a contract back on release during summer of 2010. Kept it right up until fall of 2015.
First 3 years were great to me, 4th year I felt the slowness, 5th year it was time to go. I waited for a good deal on craigslist and bought a iPhone 6 right when the 6S released.
I got it for$350 and well worth it. Other than speed, there was nothing really I wanted from the 5 series phones. But the 6 made me fall in love with my iPhone all over again. Granted back when I bought the iPhone 4, Android phones were not even viable, nowadays, phones have plateaued for the most part, there are no GIANT differences.
That being said, the iPhone may not have every bell and whistle and minor piece of technology, gimmick or not, but it has 95% of them, and does it all smoothly. In my experience, androids phones tend to slow down after a year or so with all the bloatware thrown on top of Android by the phone manufacturer. Your familiar with the device, I’m sure you have backups, so when you get your new one, all your icons, messages, wallpapers, etc will go back just the way are on your current phone. Go get yourself an iphone!