Sometimes there is a premium, sometimes not.
For example, Roissybus runs 8,30€, so 16,60€ roundtrip. The difference between a Zone 1-2 coupon hebdomaire and a 1-5, is less than 15€.
The difference with Paris Visite are ~19€, but if you are planning on going out to Versailles or something, that is in 4.
BillJ