Help... Anyone else have this issue and found a solution, or has a solution even if they don't have the issue?

One little snag though is where I want to restrict access to particular forums based on the wp simple membership level.

I don't think this is a wpForo issue. As far as I see this plugin should restrict access to certain page. wpForo page is a simple page. You can disable wpForo plugin and check it again with an empty page (just leave some text to make sure the content is hidden).

I know I can use the user group permissions within wpforo but this will require me constantly cross checking for any changes to the paid memberships.

This issue is fixed in next wpForo version. wpForo usergroups will be synchronized with roles, so each change of User Roles will automatically change the Usergroup.

Regarding the first point you have responded to, I can restrict user access to the whole wp-foro forum using the wp-simple-membership permissions because I have a page in my pages list for forum top level. But there are no pages list for sub-forums.

Sure, subForums are not a separate pages. All Forums, subForums, Topics and other forum parts are loaded in the same Main Forum page. The whole forum is a one page. So the deeper restriction can only be managed by wpForo usergroups. So you should wait for the next version to have a synchronized Role - Usergroup system.