"Standard sources" don't have their trip expenses paid by the Agency.
And it DID matter if he was sent "by the Vice President" as he claimed (plenty of open sourcing on this issue showing Wilson lied) ....or not.
Being "sent by the Vice President" would open a few doors for him in Niger and give him an aura of authority in his dealings with the Nigeriens and the US Embassy in Niger...not to mention bolster Joe's importance to the Administration when he boasted about his Niger mission to journalists.
And make the Veep look like an idiot (Wilson's GOAL!!!).... for ostensibly sending a messenger to Niger and then ignoring his message.
This issue, I believe, was what got Scooter Libby involved and probably lathered up. "Who is this guy Wilson who is claiming he was sent to Niger by the Veep?"
Do we know what expenses, if any, were paid by the agency?
It was definitely Wilson's goal to have this come back on Cheney, I agree. He wanted to make Cheney look like he knew the SOTU "16 words" were incorrect, that he lied to the public to go to war.
But he didn't say that Cheney sent him. He said that Cheney's office asked for the info and the CIA sent him. Various media morphed it into him saying Cheney sent him, which isn't helpful since it's so easily disproven.