I wouldn't worry about art, Fiv. Nothing else in FL is ascii pretty. Making your moons the exception would be a point against them, imo. A sentence or two of description could go a long way.
As for the moons actually affecting spells.. I'd rather (edit: again, this is imo - don't take it as my decreed law) see spell effects on the one-two-or-three percent increase/decrease sort of scale. The munchkins will have their perfect time, the players will have their moons, and the whiners won't have anything to really whine about.
More editing: Instead of focusing on art maybe you could think about the subtle differences these satelites have in their orbits. Aligning once every 10th millenium doesn't lead me to belive that the moons have simple circular orbits. As the moons come closer to (or move away from) this event their waxing and waning would be near things with two or three moons at the same phase every night. Having one moon rising a night while the others are in their new or half phases would indicate a halfway sort of period in this cycle. Hell, do we even have an in-game indication of when the last time this thing came about? The 2.0 shift? Anyway, making the moon's positions perfectly cemented into the code might be going the same direction as making ascii art. Thus, making all of what I just wrote into stupid drivel.
Wow, this is hard work, I tell you.
