I think the issue is that when these cards were released and you shelled out the 800 and some dollars, the emerging WarpUP vs PowerUP thing only served to further fracture what was a small market for PPC ports. This was disappointing to those of us who had shelled out for the new cards. Having one of those cards (I had a BlizzPPC 060/603 in a micronik-based tower) certainly was a blast, don't let anyone fool you, but I agree that today - other than to say "my amiga is 100% classic") - it doesn't make a whole lot of sense.
It also depends on whether you are in the camp who likes the tight classic OS vs "let's make a modern amiga OS," which IMHO that ship has sailed.
If you ran a properly configured 3.1 with all the flashupdates, memory speed tweaks, rom imaging, etc, and you had decent patches for software to use the PPC, it was a nice system in 1999. If I still had mine I wouldn't use it to run 3.5 and onward.