Adam, I'd agree with your take on Valhalla. Tom has already said it doesn't reach 6 for him though. I'd be surprised if Olde Stone would, and I don't think Dale Hollow, Champion Trace, or Old Silo would even get serious consideration from him.
Here's the question I always have when the Doak Scale comes up though: Is Tom Doak the only person allowed to score on it, or is it simply a scoring system he originated that anyone can use? I've always thought of it as being like the Pythagorean Theorem. Pythagoras may have been the guy who proved it, but anyone can use it and I suspect even he sometimes forgot to carry the 1 and miscalculated (like Tom did on Valhalla). From past interactions with Tom, I get the idea that he would disagree and argue that he's the only person allowed to rate on the Doak Scale.
In the context of this thread, I guess if Doak doesn't score it a 6, it's not a 6, even if I would score it a 6 using the Doak Scale myself. Is that too confusing?
If I were scoring, I mostly agree with Philip. I'd rate Idle Hour a solid 7, and Valhalla a solid 6. For me, Champions, Old Silo, and Dale Hollow are all 4s. All are really fun courses that I really like, but I can't think of anything particularly significant architecturally about the 4s. Most golfers I know would really enjoy playing rounds on any of them, and I think architecture students would enjoy them but wouldn't find anything that they hadn't seen before.