"... MPs should fully account, with receipts, for all the money they get (as journalists have to do for all items they charge)."... did you ruin perfectly good leg-wear with a laughter-induced bladderful?
I know a great many journalists, and let me tell you now what they all know: Fiddling of expenses is a complex artform at which these reptiles excel. Most MPs that I know (and I also know a few), manage complex expenses in a way that will not bankrupt them - while not obviously dropping them in the shit either. It is also a complex artform that involves striking a balance between not having to spend the rest of your life detailing your tedious finances, and getting your operational bills paid.
If you are possessed of low cunning, a willingness to do as you're told, an imperviousness to low-level ridicule and a willingness to listen to endless cant squared, then you will make a good MP. But most MPs that I know would turn those attributes into a much larger salary elsewhere than the one they get in Westminster.
Yet MPs get written about in newspapers and weblogs. They get dissected. Their costs get examined in great detail. Yet they exercise very little other than formal power. A modern variation of Bagehot's dignified constitutional players.
On the other hand, newspapers influence public policy in a huge way. They invest less, influence more, and offer a lower quality of service than ever before. They generate a level of scrutiny that they never turn on themselves. And - outside of the PR industry - the reptiles concerned would struggle to earn a crust.
Pressure groups do the same - with even less integrity, if that were possible. And Think Tanks are a relatively new phenomenon, but they enjoy many of the benefits that hacks and lobbyists enjoy. Moral highground. No responsibilities. The joys of negativism. Full of bright ideas that everyone likes, but that no-one would implement if they had to be judged on the results.
And they get little by the way of scrutiny. Still, great oak trees from little acorns grow.