I think it's probably a case of "you get what you pay for" to a certain extent.
That being said, I'm not convinced that Blichmann's Therminator isn't overpriced. I have a Duda Diesel 20 plate chiller (http://www.dudadiesel.com/heat_exchangers.php
), and I only paid 60 bucks for it.
Relative to my old immersion chiller, it's completely insane. I can basically cool my wort very close to the cooling water temp a little slower than I can gravity feed it through the chiller. So for my last brew (a lager), I got the full 5 gallons down to the low 60's (where my water was) in about 10 minutes.
I think more plates would allow for faster cooling, but I'm not convinced it's worth the money. They have a 30 plate beer chiller that purports to chill a 5 gallon batch in 2.6 minutes, but as it is, I can't feed it that fast.