Well an A4000 could fit the bill for what I had in mind - except it was ridiculously expensive. I'm not sure why this was - presumably the Zorro slots(?), in which case I think a machine without those, and a lot cheaper, would have been worthwhile.
I mean, you could upgrade an A1200 with hard drive, CPU and RAM (and possibly CD ROM), and still get something for cheaper than an A4000/030. If these things had come as standard, and made use of cheaper 3.5" IDE, it'd surely have been cheaper still. Plus the money would have been going to Commodore, rather than 3rd party companies. Also, if things like CD ROM and memory were cheap optional extras, it would have raised the base level, and made software companies more willing to develop for them, instead of writing for a basic A1200 that maybe had a hard drive.
@NightShade737: I think he meant an extra 512K memory of Fast RAM - basically a small cheap extra amount that may have helped get the speed up.