After being nervous about switching from single to 2hand casting for a long while, all I can say is that it is a lot more intimidating than it is difficult at least in terms of a double spey and circle C/snap T (not sure there is a difference between the two) when using a skagit line. I believe both are considered easier casts but they will get you fishing in short order and are easy to learn. A couple of guys from the forum had me on my way with a few quick tips at the spey clave last year on the Cape.
Some of the casts required over your opposite shoulder when you are dealing with wind and current direction can be a bit tougher but the basics remain the same and some one with your single handed rod experience will be able to pick up on the nuances quickly. Learning to cast with your opposite hand is much easier as well.
Some guys like to boom out 100+' casts and I don't blame them, spey casting is beautiful to watch. But I think that on our smaller NE rivers like the SR, line control and slowing down the swing and getting to the right depth is the bigger challenge, not casting.