Plan permissions per individual is a needed feature of bamboo. Based on the current observation with the version 9.0.1, there is an issue with assigning individual permissions through Bamboo Specs, even though we can assign the permission, if we are directly creating the plans through Interface. But with bamboo specs this configuration not getting effected.
As a workaround, what we can do is to use the group privilege option and create groups and assigning the needed users to that group and configuring the Bamboo Specs with the below configuration will do the work.
In the above sample, those who logged in will have the view access to the plan and those who in the group <GROUP-NAME> will have the admin privilege. This can be modified based on the need.