I think I may be alright with a 16 GB model. I don't play games on my device, I've never played games on my smartphone. The most I do is stream stuff via NetFlix on WiFi, stream Slacker Radio, or play music that's stored on the device itself.
With the 32 GB MicroSD card that I have ready for the device, I figure that I'll have more than enough room for my music and other things.
I have a 32 GB Galaxy Nexus, 28.13 GBs of it is usable but I have 24.51 GBs of it that's available for use. Most of it is pictures, video, music, and some random downloads; all of which can live on the MicroSD card. Only about a GB of data is for apps and related data.