Sure, NASA should produce truly revolutionary designs. I, too, was initially dissapointed by the appearance of Constellation.
But then, they'd need lots more money from Congress than they are getting now. Lots more. If the money from Bush's Mesopotanian (mis)Adventure had been plowed into NASA, we'd probably be on the verge of actually *profitting* from space travel.
Alas, that's never going to happen.
As for cost - The cost of launching the Shuttle was ridiculous. Each "space truck" had to be extensively (and expensively) refurbished after every launch. More fuel was needed per launch, because the re-useable Shuttle massed vastly more than an equivalent disposable capsule would. And it was further limited by this extra weight in that it couldn't reach much higher than Low Earth Orbit.
Our materials science and engineering skills just aren't up to producing vehicles that can survive the extreme stresses of a space launch, and still be light, reliable and durable.
Oh, I'm already talking about the Shuttle in past tense, which is jumping the gun a bit. But not by that much...