I'll play. In my view, Aggression and Finesse do not live on the same axis. Instead I would say that at one end of the axis lies what you could call aggression/direction, and on the other lies perception/reaction. They are both valuable, as @segbrown and others have pointed out nicely.
Think of skiing as a kind of board game. You have a pile of cards that I'll call "Resources." They can be external (good skis suitable for conditions, quality tune, excellent boot fit, appropriate clothing, goggles that aren't too scratched) or internal (strength, flexibility, sharp eyesight). Some of these can be bought outright (skis). Some have an innate component but can be increased with effort (strength, flexibility), but are not skiing talents, per se. Edit: Good snow conditions - or not - are part of this mix.
You have another pile of cards that I'll call "Skills." These are always internal, and utilize the Resources in the other pile as needed. "Skills" include things like ability to tune your skis to conditions and preference, ability to choose appropriate clothing for the weather, smarts regarding evaluating boot fit and its effect on your skiing. More importantly, they include all the many technical things that the instructors on this forum like to talk about, such as the ability to vary edge engagement at will, at different stages in the turn, from fully locked to a greasy nearly-flat-ski slide, or to flex and extend at the right moments in bumps or in a carved turn. They will tell you your sharp eyesight won't do anything for your skiing if you're using it to look at your ski tips.
Significantly for this discussion, knowing how to apply aggression in your skiing is a Skill. For example, while there are certainly subtleties to coming out of a start house with the maximum speed and momentum before you trip the wand, you will never be really fast out of the gate if you do it as if you were painting a watercolor. Instead you need to direct events emphatically on your timeline and on your terms. You need to learn to be aggressive. If you have the "strength" card in your Resources pile, so much the better! But if you don't, you still need to be aggressive. The ability to deploy aggression in your favor (a Skill) and physical strength (a Resource) are not the same thing.
Similarly, you cannot ski complex trees well, for example, or an icy course, if you try to overpower them with brute force of will or body. Instead you need to be perceiving not projecting, listening not talking, reacting not directing. The racer, milliseconds after blasting full bore out of the starting gate, may need to apply a relatively light touch on the first turn in order to stay clean and sufficiently early on a really hard surface (or not to slow down too much on a soft one). Now painting the watercolor is exactly what is needed. If you are fundamentally a receptive, thoughtful, careful perceiver, so much the better! If your skis are perfectly suited and tuned for the conditions, so much the better! (NOTE: If you are really strong here, too, so much the better! It's not the Resource; it's how you apply it. Strength may be applied in the service of delicacy as much as in the service of power! So sayeth the sages of the millennia.) If you don't have these, you still need to do the best you can with what you have. The ability to apply lightness of touch (a Skill) is not the same thing as having the perfect Resources at hand.
To me, "finesse" is neither aggression/direction nor reception/reaction. It is the master skill. It's the art of applying cards from the "Skills" pile in a way that makes the most of the "Resource" pile, irrespective of whether it's meager or well-stocked. It's knowing how to modulate, instant-by-instant, between thrust and parry. With this definition in mind, I would say that finesse is what makes a great skier great.
Edit: Obviously we need a Meyers-Briggs of skiing!
Edited by qcanoe - 12/27/13 at 7:54pm