Spending money to get more eyes on the design is not necessarily a bad thing. Okay, it's probably not worth wasting money to start training astronauts (which Mars One is supposedly going to do this year) since we already know how to do that. But design studies tend to build on themselves. For anybody keeping score:
Mars Direct: the original mission to Mars plan by Robert Zubrin, which included a return flight, first developed in 1990 and expanded upon in his book The Case for Mars. Elements of this plan, which Zubrin proposed to replace the full-up, half-trillion dollar, new-development-for-everything Mars mission developed back in 1989, have been incorporated in pretty much every design since then, including Mars One and NASA's Design Reference Mission.
Mars for Less: a modification of Mars Direct that used currently available launchers -- not relying on a Saturn V-class rocket like the original Mars Direct or Falcon Heavy like the others (including a modified Mars Direct). One criticism that came out of this that also applies to Mars Direct is that the estimation of aerobraking was too optimistic.
Mars to Stay: a more generalized policy that says any mission to Mars should plan for permanent settlement, with only an emergency return system. Supposedly there are more concrete designs out there, but they don't seem to be readily available. They seem to advocate going more through the official channels, with the hope that the US Government will pick up the tab. I believe /. had a few discussions about this when Buzz Aldrin spoke in favor of one-way missions. A lot of the latest designs, including Mars One, have picked up and ran with this idea.
Mars One: the project by Dutch entrepreneur Bas Lansdorp. This year they're supposedly going to select 24 astronauts and begin training, and they claim that they'll have 20 of them on Mars by 2033. Note that Zubrin has looked at this, and he is quite doubtful at their ability to raise the necessary funding (which relies heavily on merchandise, advertising, reality TV, etc.).
Those are just the proposals that are getting lots of press, or have impressive people backing them. There are tons of others that are just as far along (only paper designs), e.g. by MarsDrive, DevelopSpace, etc. And of course you also have Inspiration Mars, which is Dennis Tito's plan to send two astronauts on a flyby mission in 2018. Maybe it's hype, but Mars One does feel like it's a bit further along since they aren't waiting on government funding to move ahead with some aspects of their plan. Although, Zubrin's own Mars Society has bitten off small chunks of necessary development, such as the Mars Analogue Research Stations  and .