I never saw much need for vanilla syrup (with so many other ingredients, including most brown spirits, having strong vanilla flavors already) but after working with it in my bar I have to admit it has its uses, particularly when paired with white spirits that don't usually get the barrel treatment (kirsch here, but also genever).
This drink was inspired by a sour from Momofuku Ssam Bar that mixes Smith & Cross with a touch of Laphroaig and a house-made vanilla-clove syrup.
Finally, yes, something worthy of the vanilla superfine sugar I made a while back (figuring it's easy to turn it into a syrup in a moment). This is one of those things that is so good that you just kinda giggle at first sip. I think I made my syrup a bit on the saturated side, but whatever: those little flecks of vanilla bean floating on top are so lovely.
Also, maybe I'm boneheaded not to realize this sooner, but pouring over the soda holds the froth from shaking very well. I won't forget that trick. Thanks!