When a user notices a featured Meta.SE topic in their own site's sidebar that impacts them, and they click through to Meta.SE, a significant number of them, regardless of their expertise in their subject and site, cannot show their disagreement with the change by downvoting because they have not already participated in Meta.SE enough to downvote.
The results of this user disenfranchisement are clear. You have announcements with an upvote/downvote record of 594/124 while the highest voted response is negative towards the proposal, and has 629/26 votes.
It is then trivial to assume that because the main post's votes are largely positive, there must be significant support for the proposal, when the reality is that there is significant unhappiness about the proposal, but we've disenfranchised users so they are unable to express it appropriately. Further, we cannot simply assume that the 629 negative cancel out the 594 positive and assume half the people don't like the proposal because it's possible to vote positively for the proposal, then after reading the later discussion changing one's mind and being unable to change their vote on the proposal until someone edits it (they certainly can't edit it!).
While there are some work-arounds, such as hosting discussions on individual metas and trying to bring those responses to the table, as well as upvoting the negative responses in the hopes that people they trust pay attention, this is inadequate. In such cases people still assert that there is more positive support for such a proposal than negative disapproval.
Meta is actually another Stack Exchange site for experts about Stack Exchange, and so it makes sense to have some bars for participation in terms of how new users can contribute and gain reputation.
As you notice, though, there are things discussed here that have significant, direct impact on other sites.
Further, downvotes on Meta are often used to indicate disagreement - in the same way we originally used Uservoice to prioritize features and express agreement and disagrement. To some degree it's a priority queue, but it's terribly unbalanced if the vast majority of our users can only put positive pressure on change proposals.
Conclusion and recommendation
Down-voting should not be tied to the high level of reputation currently required - you don't need Meta.SE expertise to evaluate the usefulness of an idea to you or your site. On a regular site you vote according to truthiness, but here you vote according to usefulness given your perspective/experience.
Meta.SE should lower the bar for downvoting, making it equivalent to upvoting.
Because there is still a 2 rep cost associated with downvoting, this will still be self-limiting, and prevent significant abuse. Once a person downvotes significantly, they will have to also participate in other ways to continue to downvote.