You can pipe Get-Mailbox to Get-MailboxFolderPermission (in Exchange 2013, at least), but it only returns results for Top of Information Store, not the Inbox. Therefore, I'd also agree that you'll need to utilize ForEach-Object so that you can append :\Inbox (or whatever other folder name), to the alias.
In my personal experience I've used get-mailboxfolderstatistics to get mailbox folder id's (folderid property) as I've also had to deal with folder names with Unicode characters. That one is :
for the identity parameter of get-mailboxfolderpermission