DVDSP
If you're going to publish DVDs, I highly suggest using 2 pass VBR. VBR is the true advantage of DVD. Constant encoding rates are fine for music (with constant changes) or very static video, but with any movement in the video, VBR will make a huge difference in your videos.
Although I haven't used DVDSP yet, VBR is what allows a major blockbusters to look good on DVD. With VBRs, quick movement on your videos looks great, and slow, static images don't take up much space.
Eventually, DVDSP features will reach mainstream applications, like iDVD or FCPe. But for now multi-pass VBR requires is a ton of rendering and most consumers simply aren't interested in subtitles. $250 is the academic cost, so I assume you're like me and still in school. If nothing else, get it before you leave school.
If you ever do professional productions you will want them to look great on DVD, because that is probably your main distribution method. And VBR and subtitles will make a serious impact and look much better than iDVD.
Just my 2 cents,
W