Here's my take on it. You can buy the bigger ipod but chances are pretty good that Apple will come out with a newer design and you'll want that one. I went with the 3rd gen ipod nano 8GB. I can keep up to 2000 songs on it (or in your case the 4GB will hold up to 1000). When a newer design comes out that I have to have, I can buy that one without feeling guilty for dropping tons of money.
Also, Apple will have undoubtedly come out with a new style before you can fill that 30 GB up!