Doesn't seem like a wild bet to say that Space Adventures could go on finding one or two customers for Soyuz trips to the ISS each year for decades even if prices don't come down: Space Adventures Announces American Software Developer’s Plans for Orbital Spaceflight Scientific Mission - Space Adventures - Apr.3.06.

But what if prices for orbital trips did come down to $1M or $2M? Seems like it's gradually going to become obvious that there are tens of thousands of customers worldwide who can and would pay that much. (There are millions of millionaires in the US alone.) This means there are billions of dollars to be made by the first companies that can sell orbital tickets at such prices and maintain good profit margins.

Some companies are starting to think that far ahead:
* Hotels in Space: Another Giant Step for Branson - Hotels Magazine - Apr.2.06 (Via New Voyage News)

Whitehorn said the Spaceship Company would not start work on SpaceShipThree until after 2010. It is intended to be the worlds first commercial orbital spacecraft with potential to dock with space hotels. He said: SpaceShipTwo will be the testbed for a future spaceship which will be capable of orbital flight.

* Rivals race for UAE launch space: Virgin Galactic and Space Adventures eye Ras Al-Khaimah as potential base for suborbital tourism flights - Flight International - Apr.4.06

Virgin Galactic has increased the size of the SS2’s carrier vehicle, White Knight 2, to the size of a Boeing 757, while SS2 itself will be the size of a large-cabin Gulfstream IV business jet, designed to allow space tourists to experience weightlessness and spectacular views.

I'm guessing that the WK2 is this big so that it will also be able to carry the SS3.