I can see that working on store bought extracts in an alcohol base. Boiling out the alcohol (Reduction) concentrates the flavoring. It's very similure to extracting
tobacco flavor with alcohol. With tobacco we reduce it to about 65 - 75% of it's original volume which makes the flavoring about 75% stronger allowing you to use far less of a percentage. The same process would hold true to natural flavorings in an alcohol base. Just as a word of caution do not use any flavors with oils, gums, additives or sugars. This can cause a health risk but what you did with pure vanilla extract I only see an up side to it.
Good job, I think you hit on something that could be of great benefit to a lot of folks around here.
I've done many alcohol based tobacco extractions from raw tobacco leaves and although I don't use store bough flavorings I never thought to try that. I think this thread will spark a lot of discussion and experimentation.
Note to anyone wanting to try this, besides my earlier warning above only use natural extracts in an alcohol base. PG bases will be a waste of time as evaporation will be next to impossible.