In the case of Pluto's high-resolution photos, there are maybe billion dollars behind it and hundreds of people that worked for years before actually the photo has been taken.
I only mention it to underscore that our intuition on the cost of NASA is often wrong. You see a lot of people complaining about the relevance of spending on NASA, when they actually represent a very small part of the overall budget and they spend the money very well.
In contrast, Facebook bought Oculus for $2 billion, tried to buy Snapchat for $3 billion, Microsoft bought Mojang for $2.5 billion. Maybe it's a sign we aren't taxing them enough, if apparently there is enough money to go around for toys but not NASA.
[0] http://www.thefiscaltimes.com/2015/07/14/Here-s-What-It-Cost...
For $720 million, they built a half-ton spacecraft, launched it into space, sent it on a path out of the solar system, tracked and guided it all the way, and had it gather about a million times more data than existed before about a particular small icy body billions of miles away.
To put it into perspective, that's about what it would cost to buy two A380 airliners. Two. You can buy two airliners that are not much different from the ones that existed 40 years ago, but that happen to be somewhat larger and carry some more people, and then have to spend even more money to operate them, or for the same money NASA can do an entire mission to Pluto from start to finish.
Or for a different perspective, for the cost of the B-2 program (an airplane which basically never had a mission, whose key feature probably doesn't work anymore, and which in any case is far too expensive and precious to risk in any environment where there's the slightest chance it could be shot down), assuming costs would be the same as Pluto, NASA could send seven missions each to every planet in the Solar System including Pluto.
For yet another perspective, it's about 1/9th the cost of the Washington Metro's Silver Line product. So, one mission each to every planet in the Solar system including Pluto, or 60 miles of railroad track and 11 light-rail stations.
It's not a sign that people aren't being taxed enough, it's a sign that NASA is a bastion of amazing efficiency and capability in a sea of unbelievable waste.
Oh man, I would love to try VR in zero-G. I wonder if the visual ground reference would take over for the lack of vestibular ground reference? ZOMG! There is science to be done!
They create demand, which means people work to purchase them.
That work brings value to society (person x helped build a bridge, y did a dental implant, z built a yacht (horrors, a toy for a rich person, but recursively read this post)).
This is how economics works. You can't artificially split out some random activity, decide it is 'frivolous', and tax it out of existence. We are creating things, not destroying things. Dollars spent do not disappear, they are leveraged and multiplied via the labor of millions as they pass through our hands in an elaborate dance of IOUs. A dollar bill is a chit - a promise of later labor.
For an extreme example, imagine that every day I hire somebody to move my wood pile to the other side of the house. After two days I'm back where I started, but I've wasted a person's labor for two days. The dollars I paid them didn't disappear, but we've lost whatever useful activity they might have done during that time.
Not all work brings value to society. Just because someone is given money to do something doesn't make that something useful. On the other hand, just because something isn't of value to society doesn't mean it should be prohibited or taxed out of existence. And determining whether something is useful to society is really tough, so we shouldn't assume we can figure it out. But saying they "create thousands of jobs" and "dollars spent do not disappear" isn't a good argument for these things.
Ponzi schemes for example are illegal. Gambling creates no net value so it is tightly regulated. Cigarettes are a net drag on society so they are highly taxed.