in a worst case the benefit running a contract is so small, that the fee has to
lowered close to zero, to make it usefull/profitable. in this case you have a huge
eth surplus and price will go down, no matter how many decimal points you have.
The fees can never be zero. For example if someone is selling storage (disk space) , he would want the money. He will never accept "zero" as acceptable fee for his service. This would also apply to all kind of other services and applications. It all depends on adoption. If there are millions of users, and apps, and services, there is no reason why the prices won't go higher than IPO.
Also, regardless of it being a used as "fuel" for contracts (and transaction fees), it will also be a defacto currency on the platform.