The Mac Pro is a workstation class machine, thus comes with error correcting memory ($$), dual CPU socket motherboard ($$), and Xeon class processors ($$). So, it's not surprising that a Dell desktop machine beats it in price. If you priced it against the Precision workstations Dell sells, the prices would more evenly match up.
If you compare the Mac Pro to the not-quite-comparable Dell Precision T7400 line, the prices are far more in line with one another. A stripped T7400 and a stripped Mac Pro come out about the same. The trick is that I don't particularly need "server-grade" parts for my desktop computer, so it would be nice to save that money and spend it elsewhere.
New iMacs, and Mac minis are due out any time now. 10.5.6 already has drivers for them. And odds are, they will all be able to drive a 30 inch LCD.
That supports my option of just sitting on my hands and waiting. If there was a future Mac mini with specs comparable to Apple's current MacBook machines and a 30" DisplayPort monitor, like the current 30" but brighter (and hopefully with a non-glossy option), that would be perfect.