The geometry of it being a road bike is most likely why it feels better than your hybrid, followed by the fact that it is steel. The quality of the steel has little to do with it, as this affects the more personality of how it rides versus a cheap "gas pipe" steel frame. I still say to stay away from aluminum personally. If you look for a new bike, also make sure it's closer to a traditional road geometry, rather than aggressive. A frame for hardcore road riders will have you more scrunched in and aerodynamic with your head lower to the ground, but I think what you'd rather have is something that is responsive, yet more suited for distance touring, which vintage frames tend to be since they sit somewhere in the middle of modern road and endurance fitment. It'll also have you a bit more upright so that it's easier to navigate city traffic. There's still manufacturers that make them in this style, so you don't need to be tied to looking for something that is 30+ years old. Geometry is a big reason why people like those bikesdirect models like the windsor so much.
Buyer's guide: bicycle geometry
When i had my frame made, I asked my builder for a traditional road ride quality, but with a bit steeper seat tube so that I could sit a little more over my cranks, so that I could put a bit more power into my pedal. This sacrificed a wee bit of long term comfort for better off the line action, while still giving me a comfortable and responsive ride once I got up to speed.
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