The haggardness of poverty is everywhere seen contrasted with the sleekness of wealth, the exhorted labor of some compensating for the idleness of others, wretched hovels by the side of stately colonnades, the rags of indigence blended with the ensigns of opulence; in a word, the most useless profusion in the midst of the most urgent wants.Jean-Baptiste Say
Unless I'm mistaken, the filibuster is not law, but rather a Senate Rule.
In addition, it's pointless to use the number of cloture votes in an attempt to draw any conclusions about the changing perception/use of the filibuster over time. First, the number of votes needed for cloture was 67 until 1975 when it was reduced to 60. Second, the reason the number has fluctuated so wildly in recent years is because whether or not something counts as a technical filibuster depends on whether a Senator brings something up for a procedural vote. Since 99% of the time everyone knows how the vote will turn out, Senators don't make cloture motions that they know will be doomed to failure unless they're doing so for political reasons.
Think about it - if you were part of the majority and wanted to paint the minority as "obstructionist" in order to score political points, what would you do? You'd take a few dozen bills that you know would never win a cloture vote and bring cloture motions on all of them. They all fail, and BOOM! You've got a ready-made headline: "Obstructionist Minority Filibusters Record Number of Bills."
The Senate's practice of allowing a "secret hold" largely stems from the Senate's tradition of congeniality. Senators are generally pretty nice to each other, unlike House members, so they cut each other some slack. If anyone really starts abusing it, it can be overruled by a cloture vote, just the same as the filibuster.
There's nothing wrong with either of these practices.
People sleep peaceably in their beds at night only because rough men stand ready to do violence on their behalf.
It was the Austrasians, that hewed on bravely through the thick of the fight, it was they who found and cut down the Saracen King.
Gregory Koger, Explaining The American Filibuster : NPR
From what this story tells me is that technically they can change the filibuster rule (or any rule) with a 51 vote majority if the proper procedures are followed. Personally I hope they don't because while they will get what they want passed, so will the conservatives, causing wild swings in legislation. The filibuster, while abused, does provide some stability.