Wearing a wig in religious Jewish circles is part of the understanding of hair as akin to a "private part" on the body, constituting an arousal to men (Brachot 24a). While most of the talmudic rabbis had no problem seeing a woman's hair or hearing a woman's voice, we are nonetheless told that Jewish women, being modest, would not go out in public with their hair wild and loose. As a self-imposed stricture to encourage tzni'ut (modesty), we can understand the desire of women to de-emphasize their sensuousness, to avoid being reduced to mere sexual objects.
But your question then asserts itself: is the custom a legal stricture, which following in its specifics addresses? Or does the intention of the practice, downplaying one's sensuous nature, take precedence?
Clearly, as your question intimates, there are some women who want to follow the practice - to place themselves among those who are punctilious about observing this particular stringency (perhaps to be acceptable within a specific group of women who follow this practice), yet wear seductive wigs!
Seeing how fashions change among the greater society, even regarding the attractiveness of wigs (see, for example, Lady Gaga's adoption of wigs as indicative of the dance club sub-culture), it would seem to outsiders that wearing certain wigs, especially ones more strident, beautiful or outrageous than a woman's natural hair, might seem to belie a woman's "modesty" that she might be asserting by wearing a wig in the first place.
But understanding a woman's right to define for herself her own relationship to society and the image she projects, why should other people define for her the image she must represent to the world? Perhaps it would be a sign of respect for her to allow her the leeway to choose whether to wear a wig and of what sort it might be. And it would be up to the viewer to curb his or her projection onto what is, after all, part of a woman's intimate domain.
A wig can be, if viewed in this way, both an assertion of group belonging AND the ultimate in personal choice: wig as a form of feminist empowerment. Aren't the already too many ways in which men in her life dictate to a woman how she must be?
If, then, a beautiful wig is worn out of the pathological need to belong at all costs, it might be a symbol of repression. If, however, a woman takes her idiosyncratic appearance and its implications as her own will asserting itself, even though she may be behaving forthrightly, who are we to make pronouncements as to her behavior's implications?
Cut a woman a little slack: understand that she may decide who she is going to be whether the rest of the world likes it or not.
We're here, we're fabulous, get used to it!
This is certainly one of those areas where individuality might assert itself in ways not commonly seen in prior generations. Be that as it may, dressing a certain way may or may not mean anything beyond simple preference. Such is the way of the world we live in!
Answered by: Rabbi David Bockman (Emeritus)