I don't use Propecia myself but there are a couple of possable affects of using it.
1st, More hair may improve self confidence leading to more confident and improved skiing and more interaction on lift rides.
2nd, More hair on your head will shift your center of balance upward. This will require a small, and probably worth while, adjustment. On the other hand more hair may result in wearing a hat less often, off setting the upward movement of center of balance.
Another possability, to quote Jack Nicholson from Terms of endearment, "wind in the hair, lead in the pencil". If hair growth increases, wind in the hair increases. The resultant downward blood flow may also cause center of balance issues as well as reduced judgement both while skiing and on the chair.
3rd, More hair = less glare. Skiing partners will need sun glasses less often.
Personaly my hair loss is on the back of my head. I can't see it so it doesn't bother me, other then the fear that if the reflection blinds someone up hill, I may get run over. I compensate by skiing faster.
4th, More hair means using less sun block, leading to more $$$ available for gear and lift tickets.
All in all I think the adjustments are probably worth it if it works.