I researched this same thing ad nauseum when I was buying my spotter. It comes down to this: will you be digiscoping? And if so, how important is the image quality to you?
If not, then your eyes will probably not notice the difference. I did own the non-HD model for about a week or two while I tried it on my front porch, then I bit the bullet and bought the HD. I'm that kind of guy though- there's always that thing in the back of my head that says there is something better out there, so I had to do it. I can notice a touch of difference, but not much. I also digiscope, though, so I wanted it for that.
From those that I spoke with in the optics industry, like Doug at cameraland, the majority of users won't notice the dif, and would be delighted with the non-HD.
Vi Et Armis Invictus Maneo