Metal doesn't so much stay cold as conduct heat well. Wood would feel colder than metal if it were running hot because the wood doesn't conduct the heat. Metal can help radiate or convect the heat away though - hence heatsinks. Mainly you'd use it for the style aspect but also, you can drill and tap a hole in metal and then directly put a pc style machine screw into it...although, now I put it like that, wood is rather infamous for taking er, wood screws without having to tap the hole.
Looking at the design. Apart from complaining that you could fit more rads in there and hence aren't trying hard enough
Have you thought about having the entire floor, back panel and front slide out? If the sides have rads mounted, unless you want to have those slide out - which is awkward in terms of then supporting the top - you'd have to mount the rads on the bottom but have them line up with the sides so they slide with the bottom but exhaust out the holes in the sides.
Just thinking that once you've got a water loop connected up, unless you're planning top access as well, the removable panels aren't going to give you enough access to get to stuff without ripping the water loop free unless you leave enough slack in the hoses to look bad.
Access from the top is good too....unless you're like me and have your desk cluttered in all the crap you should have neatly filed away! ...and monitors, although you could mount them on an arm.
