The issue is a little more complicated than can be expressed in a sound bite.

For instance, in this white paper the Planetary Society states:

"...nuclear electric propulsion has the property that it only makes technical sense for very large spacecraft, approximately 10,000 kg or more. Such missions are very expensive. In essence, NASA is accepting the premise that huge machines, flown not more than once a decade to a remote destination, and carrying heavy payloads will be
back in vogue when this technology has reached fruition. These craft were derisively termed “Battle Star Galacticas” by the former NASA administrator and are a sharp reversal from the better/faster/cheaper mantra that NASA has pursued over the last decade."

In other words, these missions will certainly be faster, but they will also be a lot bigger, heavier, and more expensive. Getting funding for them will be less assured and longer in duration. Likewise the development time will likely increase, so will the missions actually arrive at their destinations any faster? Will we do as much net science as we do today? Or less?

One last note: if the following (from your link) can be considered "advocacy", then we would be better off without any:

"O'Keefe (who has no formal engineering background) embarrassed himself by testifying entirely falsely to Congress that a Pluto probe should wait until an NEP system had been developed, because such a probe -- even though it couldn't possible be launched until about 2012 -- would still reach Pluto before a simple, vastly cheaper Jupiter-assisted probe.

He also stated erroneously that such a late-launched NEP Pluto mission would be far better than the simpler probe because it could use its NEP system to brake into orbit around Pluto for protracted study."