It is all Personal Preference, I own a 40D, sold my 30D, cannot say thee is a lot of difference in the build quality between the two the 40D has a better grip, more rubbery, and with the added AF button the indent to hold, is bigger and fits better into my hand
As for metal hinge and plastic hinge, if the plastic does a good as job, what difference does it make, though I use the old 30D grip, so took off battery door 
I think people are finding it hard to appreciate the new 40D is really turning out to be a great camera, and trying to find faults that really are irrelevant, looking at some of the photos from the 40D taken by people who are getting used to it show how good this camera is