Well, in term of sofware, i guess you may be right, but the AmigaOne will have the advance of running Linux, and you can also run MacOS on Linux, so you should be just fine:-). Yes, i believe the 600Mhz G3-SE is more than enough, but XE allows you to upgrade your CPU at a later date, if you wish.
The first run of AmigaOnes may not be so very impressive itself, but when they start to support DDR/DDR-2 and 4x/x8 AGP among other things, then the real fun will start:-). Anyway, the AmigaOne deserves all attention, and it deserves the chance to join the market again:-)