Modern recipes are basically what you'd expect a recipe to be - malt, hops, some spruce as an additional flavor. Historical recipes tend to rely on spruce tips as the only herb/spice, and most of them use molasses or sugar as the only source of fermentables.
You could have a very nice beer indeed if you brewed a simple ale and substituted freshly-harvested spruce tips for some of the hops. I think you'd have a wonderful beer-adventure if you brewed a recipe you know well, one you've brewed before, and subbed spruce tips for flavor and aroma hops additions.
If you choose an historical recipe, that's easy. Here's one from my files.
Take 7 Pounds of good spruce & boil it well till the bark peels off, then take the spruce out & put three Gallons of Molasses to the Liquor & and boil it again, scum it well as it boils, then take it out the kettle & put it into a cooler, boil the remained of the water sufficient for a Barrel of thirty Gallons, if the kettle is not large enough to boil it together, when milkwarm in the Cooler put a pint of Yest into it and mix well. Then put it into a Barrel and let it work for two or three days, keep filling it up as it works out. When done working, bung it up with a Tent Peg in the Barrel to give it vent every now and then. It may be used in up to two or three days after. If wanted to be bottled it should stand a fortnight in the Cask. It will keep a great while.
From the journal of General Jeffrey Amherst (1717-1797)
That's two quarts of molasses per five gallons and a quarter-pound of spruce. Again, I've had the best results with freshly-harvested spruce tips. That will yield a beer with OG ~1.030. A word of warning - all-molasses beer is, he said delicately, an acquired taste. I made the mistake of brewing five gallons of Washington's molasses beer a number of years ago, and I never could quite acquire the taste for it. Most of it went down the drain.
A modern spruce beer recipe I've used before - and enjoyed much more than the all-molasses brew - calls for 5 lbs light DME, 1 pint of molasses, 4 oz spruce tips, and 2 oz low-alpha hops. Boil all together for 60 minutes. Ferment with a low-ester ale yeast. Bottle and condition as you like.
If you Google "spruce beer recipe", you'll encounter lots of recipes, mostly historical. Spruce beer was much used, especially aboard ship, because spruce is rich in vitamin C. I don't think you get that benefit from the spruce extract, plus I don't like the extract's flavor as well, so I recommend fresh. Depending on where you are, you should be able to harvest fresh growth right now. Sitka spruce is especially prized.
Besides, we're homebrewers! We should insist on the freshest ingredients we can find!