The valve covers need to come off at least 1x/yr to adjust the valves. I like the cork gaskets, and until now I've used CSP valve covers. I reuse gaskets at least once or twice. I've not needed any adhesive, but then again there are retaining clips to keep the gasket from sucking in on the valve covers I've been using.
I also wipe the sealing surfaces with a dab 'o grease (which only serves to keep the gaskets from sticking to the head the next time I remove the covers). The kind of grease is pretty much irrelevant, since it isn't really doing very much besides being a bit sticky when you are assembling things (which is a good thing). but I've never been able to stop the valve covers from weeping. I guess I'd rather have that than a 2 hour job scraping adhesive off the covers and the heads (and then still having them leak).
With the new engine, I'm running stock German valve covers and bales for the first time. We'll see how it goes.
Your mileage may vary.