I see. I'd love a 64GB iPhone, myself! It will come in time
Meanwhile, with my 16 GB, I find that a few Smart Playlists gives me "all" of my music in effect:
My phone ALWAYS has:
* My most-played songs
* My highest-rated songs (3 stars or better)
* My most recent 100 additions
* My last 100 played history
* Everything by certain favorite artists or on certain albums (even if rated low)
* All my custom mixes/playlists
That pretty much covers every song I'd ever manually seek out--and those categories overlap a lot of course.
That gives me "the best," but I ALSO have "the rest":
* A sizable random selection of lower-rated songs for variety.
* A small random selection of the worst--or never-rated--songs.
I set those two random mixes to Least Recently Played. That means whenever I play a song from "the rest," it gets dumped at next sync (or at least when it drops off the 100 history) and replaced by a different random song. This automatically cycles through ALL of my music.
In that way ALL of my music ends up on my phone. The stuff I seek specifically is always there, and EVERYTHING else will come up eventually in shuffle.
And what else is a shuffle, after all? I would have the EXACT same experience (whether shuffling or choosing manually) if I DID have all the music on the phone at all times.
You may find that a 32 GB Touch (or even your current 30 GB) can do surprisingly well if you take the time to set up a lot of smart playlists.
A side benefit: when I scroll through all artists or all song titles, it's a lot easier when only SOME of the "worst" ones are on there. Less to go through.
I very much didn't like the "idea" of going from my old 60 GB iPod--with ALL my music--down to 16 GB. But the REALITY works out just great--so the "idea" wasn't so hard to let go of after all.