I understand all of your points, but only have time to respond to one: speed.
I was doing some work yesterday in my studio and had a couple Macs going at once. I was having a problem with a new memory card reader that was supposed to "work with all computers" and was working with none.
I decided to fire up the PowerBook G3 400MHz (Pismo) which has Jaguar loaded on one partition to see it the memory card reader would work with it.
A Mac user who owns a 600 MHz iBook running 10.1.5 was watching over my shoulder and remarked out of the blue about how fast the G3 Pismo was behaving -- faster than the 600 MHz running 10.1.5.
I usually don't tell people which machine has Jaguar on it because of the NDA, but in light of these discussions I just couldn't resist.
The speed improvement was noticeable to this Mac user on a 400MHz machine. Will it be fast enough for you? I don't know. But I certainly think it's worth taking a look.