I agree with Sean about the character of the two courses seeming more like a single course in my mind (at this 3-year remove, anyway). I'm not saying the Walton Heath experience is superior to other 36-hole days but I sort of like the fact that it all blurs together in my memory.
There's a certain charm to playing the same course twice, before and after a decent lunch. And there's a different charm to playing two very different courses in the same day (it tends to create a "rush" of novelty overload). Playing the two courses at Walton Heath is more like the former than the latter, except with greater variety than literally playing the same 18 twice. But you lose the advantage of knowing where the putts break in the afternoon round...