My 128GB with my full, comfortable setup sans iTunes library is 65GB. This is Final Cut Studio (minus all of the content, so just FCP/Color/Soundtrack), Photoshop/After Effects/Dreamweaver/Illustrator CS5, Borderlands, Minecraft, Portal, Garry's Mod and a few other games....and Office '11.
I use Slink to tunnel to my home network for my iTunes library with no issue. I use Grooveshark for music as well.
If I really tried I could probably cut down on some stuff(Borderlands is 8GB!) to fit it all on 64GB, but the SSD would be full all the time.
I'd definitely upgrade, but keep in mind you can always get the 64GB and upgrade the SSD stick later.