In a FPTP winner-take-all system, voting third-party is most certainly wasting your vote.  This is not only because in such a system "strategic voting" usually results in just two major parties where those who are not members usually have no chance of winning (those that have won major offices have all or nearly all ran as independents, and were usually established politicans from a major party before becoming independent), but also because of the spoiler effect that can be caused by those who don't vote strategically for a major party candidate. We found that out the hard way in 2000.

Even ignoring the anachronistic Electoral College (no other advanced nation selects their head of state in the fashion we do) and focusing just on Florida, Bush won that state with a mere 537-vote lead, less than 0.01% of all ballots cast. However, he did not win a majority of the votes in the state, only a plurality. Had everyone who voted for Nader had voted for Gore instead, Gore would had won a slim majority in Florida. Now, a lot of those Floridians who voted for Nader might have stayed home if he didn't run, but certainly a lot of them would have likely voted Gore as Nader voters skewed left and probably disliked Bush a lot more than they did. Point being, the results would have likely been different if Bush and Gore were the only two candidates, or there was some sort of runoff system when no candidate gets a majority in the first round of voting (which was also the case in nine other states). Ideally, the Electoral College should be abolished and replaced by a national popular vote, and all federal elections should require a candidate to get a majority to win, which would necessitate some sort of two-round system or IRV system. Unfortunately, the electorate is simply too complacent and the elected too vested in maintaining the status quo to bother changing anything.

This video summarizes the issues with FPTP winner-take-all electoral systems:

Third-party movements rarely affect any real change. The last time that happened was the Progressive movement, whose efforts led to various labor law reforms that we now take for granted today. But even then, two of its most prominent figures, and the only ones to run for president, those being Teddy Roosevelt and Robert La Follette, were already established politicians from the Republican party. La Follette's run was 92 years ago. 92 Years! You could argue the Dixiecrats count as well, but they didn't really push for any big legislative changes, but rather wanted to retain the status quo in regards to civil right.

I don't really think one could say that Clinton's monetary policy was the result of Perot's stances on the federal budget, and it seems to be based on positions he held beforehand. Clinton was already talking about balanced budgets when he announced he was running back in October 1991, months before Perot announced he was running. Perot may have simply been a symptom of that early 90s blowback over Reagan-Bush-era deficits, not a cause of it. Also, Perot's stances on trade, one of his other signature platform positions, didn't really have much of an impact. Despite his warning about giant sucking sounds, NAFTA was passed with broad bipartisan support. Protectionism was effectively dead in the 90s. For the most part, Perot himself might have been a spoiler, as it seems he drew more potential Bush voters away than potential Clinton voters. Perot had some strong interest from primarily independent voters, but that largely vanished in 1996, and I don't think he influenced 90s-era politics in a meaningful manner. He was more a passing fad.