I would agree that paper is everything. I had been a dedicated Kid Finish user until I discovered Cranes Platinotype. Holy socks, what a finish. The paper starts really hard with very little tooth, but the final product is so velvety you want to wear it.
By the way I've found that clearing in citric acid first, then clearing in EDTA works most effectively for me with Platinotype.
And back to the original subject...I would assume that developing in water produces such extreme contrast because there is no restrainer. Would that indicate that a more diluted "normal" developer like Potassium Oxalate or Sodium Acetate would yield higher contrast, because the restrainer would be weaker? I'm trying to draw on experience, becasue Clay's right - Pt/Pd is too expensive to experiment with.