Yeah, sending a meatbag to Pluto would have been a real thrill for the meatbag. That last craft took 9 years. And that's only because we were able to chose the optimum orbital positions for Earth and Pluto. So, what, we gonna send Mr. Bag out for 9 years, assume he's not lost his mind on the journey and able to perform experiments for several months, then return Mr. Bag. Of course, with that kind of investment, we couldn't be sure Mr. Bag might not develop a sudden death along the way what with the radiation that tends to permeate space, we might consider sending more than one Bag.
Let's assume we choose 3 bags. Now we'll be wanting to feed them for 18+ years otherwise they'll get cranky due to low blood sugar. We'll also need a bigger ship than the small thing-a-bob we did send. That will require more fuel for speeding up and slowing down because whizzing by Pluto probably won't leave a lot of time for experiments.
There is also the problem that lack of gravity will tend to make muscles like the heart atrophy, so we'll be wanting to pack Mr. Gym-in-a-Box into the spacecraft.
There are the space rocks in the asteroid belt to consider. Admittedly, the probability of being hit is small. Then again only a small pebble will doom the craft.
We'll need to advertise for "subjects" to go on the mission: Wanted - three suicidally insane hearty individuals to go on a roughly 20 year mission to Pluto, be sure to see a lawyer to get a Last Will and Testament BEFORE you leave.