For me 16gb has always been enough. Thought about getting the 64gb iP6, but went with the 16gb once again.
My phone plan has unlimited data so I keep iTunes songs in the cloud. They are still playable even there. I utilized Spotify as well for streaming music. As for photos, I have Dropbox, Amazon Cloud (unlimited storage with a Fire device), Box, and OneDrive for automatic uploading. Once the photos are in there, I delete them from the photo app on my phone.
I stream Netflix, and Hulu+ and utilize OneDrive and RealPlayer for movies or TV episodes which I might want to watch on my phone later as they don't have a gb restriction on the file size. RealPlayer is actually great for uploading automatically any videos you might take on your phone as that's basically what its meant for. You can also easily share these videos this way with friends and family as well.
I'm not an app hog, so having a multitude of apps to manage has never been a problem. I currently have over 9gb of unused space on my 6 and have all the apps I honestly need and use on a daily basis.
I also own and use regularly a WD (Western Digital) 64gb
wireless storage. Movies, movies, documents, etc can be stored on it and assessed any time I need them.
There is virtually WiFi everywhere I go as well so when the decision on what size Mini to buy, I chose 16gb for the reasons stated above. It was, as they say, a "no-brainer".