I have experienced smells similar to what you describe in my lagers. I believe they are byproducts of fermentation, especially if you are happy with the taste. Try decanting some into a brandy snifter or other large glass, swirl, let it oxygenate a bit, see if the aroma dissapates in a few minutes. If it does, don't worry. Also, you might let it lager at cooler temps for some weeks. Fermentations at too warm temps might be a culprit. One never really knows about wild yeasties, do one. Cooler aging temps might help. I do not know of any thing you could add to enhance the aroma only.
The uncertainty of wild beast/yeasts has led me to use sulfites and innoculate with champagne yeast. I ferment at mild temps around 68-75, then cool age for a while until I can't stand waiting any longer. If my juice starts out at a gravity of 1.072 or so, I will add some sugar to get the alcohol up near wine levels. It helps preserve it and it will last longer - if I don't drink it all up that is. Usually my cider holds onto its apple aroma and taste pretty well.