Shuttle has become a sink hole, but it's the only game in town, for now anyway.
I heard that NASA get's I think something like 0.0016th of the US Federal Budget.
Even if that is not the case, NASA know that the temporary massive budgets of the mid 60's are long gone.
Pick a nice and simple CEV/launch system, you could see great savings in manned launches.
Shuttle was/is good at launching/servicing Hubble, operations with MIR
and ISS (what it was really designed for in the first place), but I'm glad that NASA are not going down the route of a similar kind of vehicle, good for Low Earth orbit and nothing else.
Tragically it took the loss of Columbia to give NASA a new focus, simply they could not go on as they were, keeping the Shuttle going for years yet, in the vain hope that a new vehicle would replace it, but only do the same job, hopefully cheaper, maybe better.
NASA is a major source of US prestige, it's innovations have permeated through industry and science for over 40 years, with not much more funding it could do a whole lot more yet.
Manned spaceflight is important, whilst much of the Solar System can only be robot explored, much can be manned.
Don't believe the hype, just one of the three Apollo J missions (15,16 and 17) did more Lunar science than dozens of unmanned probes could ever do.
We need unmanned, look what a great job those two vehicles are doing on Mars (well beyond their expected lifetimes), but really, you eventually have to send humans.
Back to Apollo, on 15, one of the most important discoveries was when the 'genesis Rock' was found, an ancient sample from the Moon's (and Solar Systems) primordial era.
The Astronaut spotted it out of the corner of his eye, almost by chance, would even a very smart robot do this?
People forget that the most sophisticated computer (and by far the most flexible) is the human brain.
But Mars just to explore?
Well getting the capability to do so also brings the prospect of exploration, later exploitation, of asteroids, many perhaps full of valuable minerals.
Ultimately, as Apollo 15 commander Dave Scott said as he stepped on to the Moon in 1971 "Man must explore."
Imagine if Columbus, or DaGama, or Cook had thought, "no, I won't bother, too expensive, too risky, too much chance of bad PR
Going back further, what if our ancestors had stayed put, in what is now Africa, a bad drought or similar could have caused extinction.
The Dinosaurs never had a space programme, where are they now?