From our FAQ
The initial value for mastercoins came out of the fundraiser
"anchoring". People were willing to "sacrifice" 1 BTC in exchange for
about 100 MSC, so it anchored the initial value of MSC in at least
0.01 BTC per MSC.
The more general answer is that Mastercoin provides a set of features
that only work with MSC or Mastercoin-based currencies, and there is a
limited number of them. So, in order to enjoy these features, you have
to own some mastercoins, giving them an independent value. The more
real world usage Mastercoin sees, the higher the value of each
mastercoin. In addition, as always, a lot of its value is currently
driven by speculators executing a price discovery process.
Specifically, mastercoin tokens are used for:
Creating derived currencies and smart property are used to create
and/or promote smart property tokens as an anti-spam measure.
Mastercoins are used as the liquidity layer for Contracts for
Difference The distributed exchange between Mastercoins and user
generated currencies is more efficient than BTC<->MSC or BTC<->Derived
exchanges - the latter require a 2 step commit process. As the
protocol evolves, more direct usages for Mastercoins may be created.
I added this last bit about token usages to the FAQ following your questions - thanks ThePiachu for this questions!