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 a 32gb iPhone so ill take a look at it and find how much space IOS takes up. In iOS settings, under general, there is a listing Capacity with shows how much space your phone has minus the iOS installation size, on my phone it appears to be about 27.2 gb, so lets use that number. assuming you don't install any apps on your iPod you should be able to store about. 27.2 * 1024 = 27852.8 mb.