Hello,
"Just a few examples: U-Boot nows has tons of configuration menues which allows you to tweak all kinds of Articia S settings (PCI/AGP), the location of parallel and serial ports & modes"
Well I'm personnally not a fan of GUI for BIOS/Firmware (so I don't really like PC BIOS as most have GUI), as for me advanced settings like that are only for people who know what they do.
And normally these people are used to command lines and scripts and for me command lines/scripts are far more powerful for advanced settings than a GUI.
And so additionnaly, command lines/scripts for these kind of advanced settings discourage normal users to tweak them and so it's help to avoid users that don't know what they do to do bad things on the BIOS/Firmware.
But that is just my personal opinion. That's why I really like the OF on both my Mac and my Pegasos, and far more than a BIOS on a PC.
But of course for selecting what OS to boot, a GUI is useful. In fact just like what my Mac do

The OF in itself is text based, but there is a graphical boot selector (you get it by pressing Alt at boot time) to select on which OS you want to boot.
Regards