I hear you Ben.Erik,
I'm more or less with you on the aesthetics. Although I don't use my Quicksilver as much as you do, it still remains my main PPC Mac.
Unlike you, my main one is running a factory processor.
That aside, my dual 1.42 MDD can pretty much match blow-for-blow with the Giga at 1.6 and is faster than the 1.8 Sonnet at some tasks. The Quicksilver is always going to be held back by it's 133mhz bus, whereas the higher end MDDs can not only take more RAM but are faster. Truthfully, if I'm going to keep using a G4 in this sort of work, it's hard to make an argument for NOT using the MDD, except that I just like the Quicksilver better!
For that matter, if I could ever get the SCSI situation sorted out on my dual 2.7, there really IS not an argument against using it for the tasks the Quicksilver now does...
There is some stuff both you and I do that is quite alike, but some stuff very different. And I do realize that an MDD will be faster where it concerns Photoshop and Illustrator, but while I use those apps they are only in support of my main use of InDesign.
My QS supports InDesign very well so I'll stick with it. An MDD would have to show a significant improvement over using ID for me to switch to it. Something to test whenever I do get an MDD.
In any case, there are two or three desktop Macs on my list for specific purposes, the MDD being one of those. I do tend to collect Macs (but of course, not to your degree) but I try to apply them to a specific task (if for no more reason than to justify their purchase to my wife). The MDD I intend to use as more of a graphic machine (PS, Illy) for stuff I do entirely in those apps. I think it will handle it much better and will get that load off my QS.