I've spent a little time trying to find out what account the official scoring system takes for wigs/makeup/dresses etc, with comparitively little success. This seems to be the most definitive:

The Irish Dancing Commission has established a 100-point scoring system for judging competitors. A dancer's performance is evaluated in four categories with an equal percentage of points in each of the categories (i.e., 25%). The categories are timing (rhythm), carriage (deportment and style), construction of steps (complexity), and execution (presentation). In ceili or figure dancing, distribution of the 100 points is 30 points for timing, 30 points for figures, and 40 points for deportment and style.

Nothing there that explicitly mentions the wigs and makeup. However, there is recurring theme of the importance of appearance, and I was particular struck by this webpage:

With St. Patricks day coming up, the children hope to show there skills around XXXXXXXX in dancing displays. XXXXXXX Academy Irish Dancers, already known for their discipline and neatness, will be performing a fundraising display for 100 people at the Masonic Hall on March the 28th, amongst other places.

Of all the adjectives I could pick to describe an Irish dance team in a regional what's-on? website, I don't think those are the ones I'd go for...