Hi there. I only read the first and last page of this thread, so forgive me if I'm covering something previously mentioned.
The 2 primary arguments for going with a Mac Pro (tower) would be the need for multiple hard drives, or for having slots available for things like really high end video/sound cards. If you don't need those two features, an iMac will suit you just fine. Really. Current iMac models have 4 RAM slots and can accept up to 16GB.
Also, Apple has an oft overlooked "Special Deals" section on their site. It's on the Store page, all the way down on the left.
Refurbished iMac - Apple Store (U.S.)
You can save a couple hundred dollars (or more) on a refurb unit. They come with the same 1 year warranty as new models, and are eligible for Apple Care. Be sure to consider a refurb, if you're still deciding. You can get a prior model "mid level" iMac for the same price as an "entry level" current model, and can end up with more Video RAM and a larger HD.
Hope this helps.