How can you possibly remember them all? Let alone have time to listen to all of them?
14.000 songs, at 5 minutes average equals 70000 minutes.
Now say you work 8 hours a day, and listen to music just 4 of them (let's just pretend you don't listen to them at home, at the bus/car, at the weekends, at nights, and so on).
So it's 4 hours = 240 mins / day = 1200 mins / week = 4800 mins / month.
So 70.000 mins worth of music = 14 months, and considering you take a vacation of 2 months per year where you don't listen to music, then you'd have 1.5 years worth of listening.
67.2 years being the average life expectancy for humans, let's say you started listening to music at 30 and you spent 7.2 years out in the wild living with a solar rechargeable flashlight and a pair of socks, then you had 30 years worth of listening, which is 15 times worth of listening to dmccloud's library, which is quite enough, right?
Now seriously speaking, most songs are 3 mins, you listen to songs since you are 12, you take 1 month vacations and on boring work days you listen 6 or 7 hours straight and on weekends you can spare 3 or 4 hours more.
Just baffles me everytime somebody asks me that question "OMG!!! Why do you have so much music??", well because I love music, I love rock and most of its sub genres and I can't stand just listening to every artist's couple single hits on the radio, I need to listen to the whole discography to get a real feel.
As for the original question, I'd get the 512 GB if it was available and costed NO more than 1200 USD
And it's just not music, I have 18 or 20 Gbs worth of apps and now start counting the podcasts and videos and iTunes U and Magazine subscriptions (average 120 MB per issue) and then you no longer wonder why 16 GB is so little.
Now, I understand most people can live happily with 16 GBs because they only have a couple "best hits" albums that they call their "music collection", they don't know what a podcast (let alone a VIDEO podcast) is, they use a couple note taking and reminder apps and let's call it a day.
As for me, I'm certainly NOT most people and sometimes 64 GB feels like too little.