From what I understand, harvesting fully mature rather than fresh spruce means less acid content in the shoots (including ascorbic acid aka vitamin c) and more resinous oils/tannins. So that means you’ll get a more winelike mouth-feel, more piney flavor and less “fruity”. With more resins, there might also be risk of poor head retention. If you’re going with my recipe above, I’d reduce the quantity of spruce tips in the boil by half and maybe add another ounce in the secondary–that way the heat of the boil will have fewer resins to extract.

Or alternatively you could try adding a little of some head-retaining adjunct grain like flaked barley.

Let me know how it goes!

The good stuff.