You already have a single handed outfit that would be perfectly suited to the North Stilly in the summer and in fact any summertime river.
The only times I can think that a spey rod would be a disadvantage: 1. on very small streams, 2. when you are on a run with trees directly overhead, 3. fishing out of a boat. Any other time a spey rod is an advantage..

Everyone has differeing opinions on whats a good rod vs whats a bad rod. The only rods I really encourage you to stay away from are the Loomis GL3 spey rods. I own the 14ft for a 9-10 and to be honest I think it is junk.

There is a glut of excellent used spey rods on the market and there are a couiple good "inexpensive" rods out there as well.
The standard cheap ros if the St criox 14ft 9-10wt Other rods are the Lamiglas Mike Maxwell spey rods. Also Anglers workshop produces some blanks that are decent and inexpensive.

What I'd say is if you are serious about becoming a steelhead fly fisher,get a spey rod.
If you don't know how much you are going to want to do it then stick with the single handed outfit you have and try to be around people who you can learn from. In any type of specialized fishing(including all steelhead fishing) knowledge is paramount!!! followed closely by skill.. After thoes two items are dealt with everything is not near as important.