There is going to be one very specific gear point where SotF becomes the best talent, and thats when you have enough crit and haste to never refresh DoTs. Though to be fair I'm not sure that we will ever have enough gear to make that happen.
But yeah, with the Euphoria changes I don't think it really is guaranteed to save you a cast in either pre-eclipse, and just the ability to combine two cds with NV and Incarnation+CA is just too good.
From what I was reading at EJ, incarnation is best pre-raid gear, SotF is best in normal raid gear and incarnation becomes good again in heroic raid gear. I think the reasoning is, in pre raid gear, even with sotf you'd have to clip dots to get them to good uptimes. In normal raid gear you have the haste required to maintain 100% (or close to it) uptime as long as you have sotf. Once you get enough haste that you don't need sotf to maintain that uptime, you switch back to incarnation and DOC for a 1 dot per cycle rotation. At least, that's how it is now. I fully expect DOC to get nerfed soon.
As for saving a cast or not, SotF will always save you a cast in post lunar/pre solar. SS and SF have the same energy, so it will always take you the same number of casts to go from start of lunar to start of solar (7 with SotF, 8 without).
For post solar/pre lunar it's a bit more complicated.
You can end with 3 possible energies at the end of solar. 110 (1 SS) and 100 (2 SS) will be the most common, but occasionally you may end with 105 (3 SS).
If you end with 110, with SotF, you will save a wrath cast if you get 1 or 2 SS post solar, but not if you get 0 SS.
If you end with 100 or 105, you save a wrath cast if you get 0 or 2 SS, but not if you just get 1 (again, post solar).
So, half the time you are guaranteed to save a cast, and the other half of the time you're much more likely to save a cast than not.