Mark
I was asking Charles the same question about 3 years ago, got the answer he gave you and I took his advice. I now have four 7.5sqm beds which have really good structure, more worms each year and better plant root systems evident at harvest time. Each bed had trenches dug for potatoes on rotation, which generates a nice topsoil tilth after harvest but has otherwise seen no digging whatever. Drainage has improved and in year 3 I am currently harvesting 30-40cm long parsnips weighing 8-16oz.
You can lay down an awful lot of high quality compost on the beds for the price of the wood, you know……