If I were you, I would test ride some new bikes to see if there is big difference between a new bike or your other bike. This can let you know a little about different frame materials and how they are put together (geometry of the bikes). With this test, you can also test out different types of components. After you do that, I think that you can then best decide what route you want to go. That is a very nice looking vintage bike.
I know that when I went from a Peugeot built with Reynolds 531 to a Cannondale 3.0 which had STI shifters, it was a night and day difference. The bike was so much faster off the line (I could get to 20 miles an hour starting at a green light by the time I got through the intersection). The bike was also much easier to climb with. I was able to get up long hills (like hightway 9 in Los Gatos, California) that I was not able to before. Now that could have all been in my head but that was my experience. The down side of the bike is that rides over 2 hours really took a toll on my hands and back, the bike really transfered the road feel to my body.
So, try some bikes out and see how they feel.