Will hard liquor extract flavors better? Maybe.
FWIW, my wife makes her own vanilla extract instead of buying it at the store, and she uses it for cooking tons of stuff. She simply takes organic vanilla beans and slits them with a knife, then pops them in a 750ml of vodka. Actually, I may toss some of that into a brew someday...
Could she extract it some other way? Sure - but popping some beans in vodka and being patient isn't a bad way to go either.
http://en.wikipedia.org/wiki/Vanilla_extract
It's how the pros do it: "Pure vanilla extract is made by macerating and percolating vanilla beans in a solution of ethyl alcohol and water."
Why alcohol? Because it extracts compounds out that aren't water soluable. Ethanol is able to dissolve substances which are less soluble in water, while at the same time the water content can dissolve the substances less soluble in ethanol. A win-win I guess you could say...
I would imagine that you could 'cold brew' coffee with alcohol at room temp far stronger than you could with hot water, since alcohol would be more efficient. Brewing the coffee longer would make it more bitter, not so with the vodka method. Medicinal tinctures are also made primarily with some type of alcohol.
Lots of folks make vanilla extract that way too:
https://www.beanilla.com/blog/homemade-vanilla-extract
If you have bought vanilla extract in those tiny bottles, you will find that this is far cheaper to make your own. A little extract goes a long way, so a 55 gallon drum of the stuff would probably last quite a while.
It would be interesting to hear from someone who works in a microbrewery as to how they create the flavors they add...
Most extracts have alcohol as their primary ingredient, and I don't see it being for sanitation reasons, but for the reasons I stated above. Soaking coffee (of cacao nibs) in water versus spirits will produce a weaker solution (all other variables being equal).
Of course brewing and cooking are two different things, since the alcohol generally cooks off in baking, etc.
I still think that pitching small amounts of homemade extract into a secondary is fine. It's not like we're putting 750ml of flavored vodka in a 5 gallon batch.
I'm sure the alcohol in the secondary will do the same, only requiring more of of whatever you are extracting from (as in more coffee beans/nibs/etc)