Unlikely, the more people are involved, the more spam on the social networks and that is what they want, their ico will be for many people.
The purpose of bounty is to makerting and the more participants they promote success
Yes, talking about the purpose for popularization of the idea of the project -yes, you are quite right. The more people mention about the concrete project in their social profiles or other resources - the better for the rising interest to the project from potential investors. But for the people, who participate in the bounty - who make the contribute to the development of the idea of the project - it is less interesting... everyone wants to get the right and attractive own benefit... May be it`s a good idea to limit the amount of participants members, but taking into account the both side`s interest.