What you might want to do is go through your files and clean out the "dead wood" so to speak. I am a DIGITAL PACKRAT and I like to have a lot of stuff on my phone....you never know when you will need it right?.
I ask myself "When was the last time I viewed those photo's?, listened to that music?, watched that video?". If it is more than a month or 2, then obviously it is just taking up space and I copy it to my laptop or if it is something I really want to keep I can dump it to DropBox I will have it at my fingertips.
I like the Google Music idea, but, if I am in a 3G area or I don't have access to WiFi, I would get frustrated.
I just checked...I have 11,588 files on my SD Card and I am using 26GB. That is EVERYTHING on my card....cache, temp, drivers, ROMS, Music, Movies, Pictures, Video's, Data.
I am constantly cleaning off my SD