I wouldn't up alcohol for aging reasons, at least not much. Though some ports will age a long time, many if not most lower alcohol wines age better than their higher alcohol counterparts. For instance French Bordeaux will almost always have a lower alcohol content than its California counterpart. However, the California wine will peak and subsequently decline much sooner than the Bordeaux.
Some things to consider with aging wines (in no particular order):
1) Quality of the grapes.
2) Ripeness of the grapes when harvested.
3) Level of tannins.
4) Acidity/pH.
5) Level of sulphites (must be enough to protect the wine for extended periods of time).
6) Temperature of storage location.
7) Cork quality.
With mead, I would start with the best raw, unfiltered, honey I could find. For tannins, you might go with Tannin Galalacool. Typically used with white wines, but should help your aging potential. You also might want to oak. Not only will oak add tannins, but you have plenty of time for the oak flavor and the tannins to mellow. I would also recommend adjusting pH down pretty low. Probably less than 3.20. With wine, acidity tends to decrease and pH tends to increase over time. I assume the same is true in meads. You should also go a little overboard on sulphites. Sulphites will disipate over time but going a little strong and having a low pH should keep you protected. Temperature of the area you are keeping this in will likely have a large effect. If you have a way of keeping at proper cellaring temperatures (52 - 57 deg F), that would help tremendously. You might even want to store cooler than that if possible. Finally, you should probably start with the most expensive, highest quality cork you can find. You should probably re-cork every 6 or 7 years.