Wow, I must be one tough SOB. I'm permanently disabled in my neck and shoulder. I still can throw a single hander all day. I do spey and single, but still prefer tossing a single. Guess I got the technique down. Not a ton of falsecasting. Usually a few good loads and out it goes. Think most get tired in the salmon/steelhead weights because they just cast way too damned much. Couple casts and away it goes. Is a spey easier to cast? Of course. But have no problems with a singlehander. I won't ever give mine up. But am getting a nice collection of speys back finally. LOL
I use a single hander most of the time. Mostly because I can't spey cast to save my life, but also because it feels more natural and fluid to me. I've thrown my spey rod against the rocks on the Hoh many times out of frustration.
My 10' 8wt. can throw stuff a mile, though, so I am rarely in a situation where I actually need a spey. I don't fish rivers that big. However, I do swing on a spey. That's actually the only time I use it.
I don't want to be constrained to picking one type or the other. I use a Spey rod for steelheading because I still learning and liking the novelty of Spey casting and can cover more water with less effort, which is not the same as casting farther. But I'm still attracted to the fluid dynamics of single hand casting that got me into this passtime in the first place, and I have no intention of ever giving that up.