The ISS should be used to test longer and longer duration flights, even if there are only two astronauts aboard and even if only Russian vehicles go there and even if most of their work involves maintenance.

One cosmonaut spent 14 months aboard Mir but his intention was to have spent 18 months. It's Thagard's flight (and US money) that prevented that.

A crew of two (US-Russia) should do that (18 months) and this would enable two things: every 6 months, a paying ESA astronaut would go up there with two paying tourists: it means that while a russian and an american cosmonaut spend the time, 2 paying professionnal astronauts and 4 personally paying tourists could go to the ISS.
The ESA astronaut would be trained to fly the vehicle, there's much more money for the Russian space program and they have the honor of breaking a record , so does the US astronaut!

Just an idea:-)

Raoul