Gerry in all honesty now.!! If you had both options available IE full Access to machinery and resources would you build from Wood.?
It would probably depend on the actual machine. If I needed a 4x8 (or larger) production router, then it would really need to be steel. For anything say 4x4 or smaller, I'd still go with wood. Mainly because I like working with wood, steel not so much. And I know how to use wood and make it work well.
As you alluded to, wood is much cheaper for me than aluminum.

The gantry beam in the pics has $30 in MDF, and $35 in phenolic, and about $15 in glue. Say $100 complete for a 68" (1700mm) long beam. I couldn't get an aluminum structure that would be as strong for anywhere near that cost. The Hiwins that mount to it were $350 (20mmx1700)

Calculations are showing a deflection of about .02mm with a 200lb load. I actually believe it will be stiffer due to may laminate construction, which appears to be about 2-3x stiffer than regular MDF.

Equally if you didn't have access to either equipment and had little to no experience using either wood or metal/Alu profile.! . . Say an office worker just looking for a DIY hobby in the back shed which of the two options would you say gave the best chance of success FIRST TIME of an accurate, reliable machine.?
I'd definitely recommend the aluminum extrusion. Or is it aluminium for you guys? It costs more, but is by far the easiest for a novice imo.

I'm with you on the CNCRP carriages, btw. Don't care for them at all.