My issue with the speed limit, and Forces of Nature as an episode, is that I really dislike what it says about man's relationship with technology. I have no problem with Trek commenting on environmental issues and suggesting ways for humanity to overcome them, but before Forces of Nature, the solution was largely one of further research, scientific development and increasing technological sophistication. Essentially, it admitted that technology can create problems, but posited that more technology can solve them, or at least kick the can down the road a long way. It's a very positive, optimistic message about our future.
(A prime example of what I mean would be The Voyage Home: "ouch, we wiped out the only species that can save us. No problem, we'll devise a way to travel back in time and bring them back, and have fun at the same time too". It's a very hopeful message and one I like.)
Forces of Nature says, "no, this problem means we have to slow down (literally, as it happens) and minimise the damage rather than find a way to overcome the problem through mankind's ingenuity". I don't believe that's the right attitude to take, but especially so in Star Trek.
Indeed, it's uncharacteristic for Trek to take a post-modernist stance; and I agree that it's not the answer to environmental issues (be they real or Trek's): the solution is better tech, progression not regression.
As an episode, Forces of Nature just ends up being filler: neither very good nor very bad.
What I would have liked to see would be an episode dealing with how the Federation is seeking to find a solution for the problem.
The episode with that warp "wave" could have been a trial of a new technology meant to resolve this issue. From what I remember, that episode did not have a specific reason other that "traveling at warp via an external energy wave is cool" idea.