Neil
There’s not a stronger authoring package anywhere close to DVDSP (PC or Mac) unless you want to step up to the more high end spec tools. I think someone said that DVDSP has nothing to do with the quality of your streams – thats the job of the encoder. If you need better result you need to learn the finer points of down conversions, encoding and menu design.
As for Compressor, its a great all around swiss army knife but its a crappy MPEG 2 encoder.
If you gave me your streams done on iDVD against what can truly be done with the right knowledge, I’ll pick out your work in a heartbeat. 🙂 Not trying to sound mean, its just the truth.