I've had zero problems with the Ritchey adjustable stem on my hybrid for the last 8 years. Keep in mind, they're available in differing lengths; match what you've got for the least change in geometry (measure from center of bar clamp to center of steering clamp).
Would changing out my stock cassette improve my speed? What are my options?
The gearing you have is good for 30mph+, which is redonkulous on a hybrid. The way to improve rider speed is to improve the rider. Are you riding high cadences yet? I'm a huge proponent of high cadences on any kind of bike.
Switching to the habit years ago was difficult, but my cruising cadence is now 90rpm's and I can hold 120 easily. It's far, far easier on the legs, and you'll find yourself rather faster using it. I have a 52/42/30 + 11-32 on my Coda, and never use the big ring. On the 42, I have no trouble cruising over 20mph in still air and 16mph into a headwind. On your 36, you'll probably be using the 4th-largest cassette cog and smaller.