I'm an IT software guy, but I was once an IT hardware guy, so I have a lot of experience with SCSI-1 and 2. The problem with them was generally compatibility. Not all SCSI card worked with all SCSI devices. Not all software talked directly to SCSI cards, but generally needed some sort of software driver to address, which was based on the OS and might or might not be available for more modern OS's. I haven't run a SCSI card since Windows 98SE, and believe me, that was a struggle with older SCSI cards. XP was basically right out for some of them, end of life. Now we have Vista - assuming one is a Windows person.
Again, nothing wrong with SCSI if one wants to dick around with adapters, drivers, and perhaps even (God help me) interrupts and reserved memory locations. I doubt most computer users are equipped to deal with that kind of nonsense anymore - I know how to do it and I refuse on the principle that it sucks and is not worth my few remaining brain cells anymore.
I haven't tried any SCSI-to-firewire adapters - might be interesting. But it is pure propeller-on-the-head geek stuff. Average person wanting to scan a photo - no way. USB and plug it in. Install drivers from CD and you're good to go. Worth $50 more? Yeah, definitely.