There's a lot of difference of opinion on what measurements are in fact the most important, and I think the reasons for most of them are at least as good as yours are. It boils down to personal preference. I think the best you can do is to ask for the numbers you want, AND for pictures, at least a side elevation that lets you see the proportions. Over time I've learned to guesstimate most of what I want to know based on that picture, combined with a few facts.

Also consider that many sellers don't know anywhere near what we on-line bike freaks know (yes, even us!), and will never give you the numbers you need. However, this doesn't diminish the desirability of what they're selling.