The great leap forward that this paper establishes is that yes Virginia, indeed the Fed went off the rails from 2001 onward (and, as many Austrians correctly suggest, was the major force behind the Great Financial Crisis), much as it was off the rails in terms of discretion from 1974-1985. I wonder what characterized both of those eras? Well, in the 1970s, of course, it was stagflation (which Keynesians still can't account for and which smashes the incidental correlations of the "Phillips Curve" to bits), while in the naughties it was over- (mal-) investment. So there wasn't exactly the same effect during the Fed's discretionary period, but this can also be attributed to the fact that the international economic world was different in the 1970s (protectionist, closed, far less integrated) than the 2000s were.
However, on the flip side, the boom of the 1980s and the 1990s appeared to be the real deal. More sustainable and not affected due to the Fed, mainly due to the lack of Fed volatility... and we all know how damaging policy volatility can be. The authors don't explore these corollary effects (they've really done enough with their econometrics), but it's an interesting area for future research.
And of course, the institutional angle on this is similar to what I explored in my Banks and Bank Systems paper last year - the institutional make-up of a Central Bank may matter less than the institutional goal of the Bank, or rather, what the inherent nature of the institution is (as someone mentioned earlier this year, an institution where you need to have a great leader not to screw up the economy is by definition not a good institution). To put it simply, Central Banks wield great power and abilities to muck up an economy, and the only way to minimize this may be via the proper policies - which, in this case, seems to be adhering to a rules-based mechanism rather than going at it willy-nilly.