The ERA is much like the proposed Child Labor Amendment. In theory, it would desirable, but in practice I fail to see where it is needed. What exactly would passage of an ERA do that isn't already being done (or least is doable by Congress if it chooses to act)? I can't think of anything.
Constitutional amendments give Constitutional basis for the passage of laws. If you've ever met a libertarian who would repeal every major legislative accomplishment of the past century on the grounds that they are "unconstitutional", then you can understand why amendments are desirable.
Because such libertarians have no power beyond their Internet strongholds?