TL;DR: Reducing respec fees solves more problems than dual spec would.
Dual spec is something that some people are asking for for TBC. Some people are against it. However, what people aren’t talking about is the actual problem(s) that it aims to solve, and/or whether it does a good job of solving that (or those) problem(s).
The Problem.
As I see it, respecc’ing maxing out at 50g/per is a high enough cost to prevent a lot of people from doing it often. Whatever the intended design decision here, whether a gold sink or whatever, it has merely only succeeded at preventing people from respecc’ing regularly.
I posit that this is not the intended feature, as further expansions have removed gold-value barriers from talent changes.
A Solution.
On the TBC Beta, respecs capped out at 50s. Even though we could basically print gold on the Beta, for some reason they decided to cap respecs at 50s. This made it very easy to respec, and even enjoyable.
Cap respecs at 50s, allowing anybody to respec whenever they want without the prohibitive gold costs.
Why Not Dual Spec.
Sometimes people make a claim that respec fees are intended to be a gold sink, and adding a dual spec feature with a fee would act as a gold sink. Respec fees only act as a gold sink if people are using them regularly. A lot of people avoid respecc’ing due to the fees, so it actually acts as a deterrent, which is a design flaw that should be corrected, not doubled down on.
Additionally, dual spec rewards some classes while punishing some others. Classes whose raid roles are fulfilled with a single spec are not required to maintain multiple builds and gear sets, and are free to use an additional spec for their liking. Other classes are required to maintain more gear sets, and additional PVE builds, rather than the “play as you like” style that can continue without a dual spec, but with lower respec fees.