Your body needs the energy to properly digest food. So to get the most out of the nutrients you consume and your workout, eat before exercising or 30 mins after fruit, two hours after veggies, three hours after grains four hours after meats and poultry.
So it's not a matter of value, it's a matter of what you need it to hold. And a matter of affordability. The movies will be the biggest space hog. So if you only put the movie you want to watch next on the iPod touch, so one (or two) movies at any given time, you will have more than enough space with either 16 or 32 GB. People watch movies once (twice if it's really good); they do not watch a movie over and over again like listening to songs.
I have about 300 songs on my iPod (Purchased MP3 and M4A with iTunes and Amazon), which takes up about 2.3 GB. So i guess you have around 4-6 GB of music, check it in Settings --> General --> Usage. Check how much space to have in 'Other' You need iTunes for that.