Yes to Spey casting...
Spey casting is usually associated with double handed rods, butÖ
You CAN Spey cast with a single-handed rod, itís just a matter of leaning new techniques, rather than giving up the single-handed rod.
Traditional Spey casting (single Spey, double Spey, etc.) involves continuous line tension, creation of a D loop with less (about half) back-cast room than for over-head casting. Many other casting strokes (roll cast, snake roll, switch, circle Spey, snap-T, snap-Z, Perry poke, wombat) have been developed to still control the line in preparation for casting in the many & varied situations you may encounter when fly fishing, and some almost completely eliminate the need for back-cast room altogether.
With the development of shorter shooting heads (Scandinavian & Skagit), Spey casting has evolved and diversified to permit generation of even smaller D loops (even less back-cast room needed), yet shooting even more line out for the longer casts. As all fly lines are cast due to the weight of the line (and not the fly), these shorter heads concentrate the loading weight for the rod performance within a shorter length of line, and they are often ideal for punching a cast out into or across a windy river (or lake, or sea shore).
Spey casting is traditionally associated with longer rods than single handed rods, but that is not necessarily the case. I know from personal experience here in the UK that it is very difficult to cast single-handed with any rod longer than 11 feet, and single hander rods may range from as little as 6 feet to as much as 10 feet. However, when you have double handed rods, up to 20 feet (maybe more) is possible, but most would use rods between 13 and 15 feet for most of their double-handed casting (traditional Spey & Scandinavian casting), but Skagit casting seems to be done often with rods less than 14 feet, sometimes down to 11 feet.
Double handed rods are easier to cast longer distances for longer periods of time without the caster tiring so much, and certainly the distances cast on average are more than that usually possible with single-handed rods (even with double-hauling), and casts of 100 feet or more are straight-forward, and with less overall physical effort by the caster.
That being said, you can still cast short lines with Spey casting with the double-handed rods, and many fish are taken within 45 to 60 feet of the caster.
However, it would seem reasonable to use a short, single-handed rod for small brooks & creeks, and where very over-hung with trees & bushes, use Spey casting techniques with that single handed rod.
It is not the case that you should get rid of the single-handed rod and replace it with a double handed rod for Spey casting, but ADD a double hander to your equipment locker, and ADD the Spey casting technical skills to your casting repertoire, and both will serve you better able to deal with more wide ranging fly fishing situations.
If people concentrated on the really important things in life, there'd be a shortage of fishing poles (spey rods). Doug Larson
Take only photographs, retain only memories, leave only a good impression of yourself, perhaps just footprints.
Your lines, your rivers, your way!