This is just my opinion and could certainly change as I am always open to experimentation. But coming to the spey thing from trout country (Rockies) my view of 2 handed rods is that compared to single handed rods they only do one thing better: swing a streamer. This because they (even the little ones) are built to launch shooting heads long distances repeatedly with less effort. They are worse when it comes to being able to react quickly to environment around you which is what you need for pretty much everything else: nymphing, dry fly fishing...even swinging soft hackles I don't get why you would do that with a shooting head, scandi included. Even for streamer fishing I am coming to admit to myself single handers are deadlier because even if your radius of presentation might be a little smaller you can present your fly in a greater variety of ways with less headache (and still jack a few long casts to swing a tailout if you need to).
But, if you have a swing friendly river and just want to cover lots and lots of real estate with repeated casts beyond 40', and you need a little bit of sinktip to get down (or wake a big bushy dry), a shooting head on a two hander is tough to beat. Sorry that's just my long version of saying that to me they are definitely a niche rod, but to me the niche is definitely not 'small nymphs and soft hackles'. Of course you can do all the other things you would do with your single hander, but in my experience having a two hander no matter how light makes all of them more cumbersome, soft hackles included.
"It is not the fish that is hard to figure out, but we the fishers, why we do what we do. For a fish survival is enough."