Currently it's intensely slow when you have several hundred subscribers. I just spent several hours cleaning up dead subscriptions - it shouldn't have taken that long. I could go make a snack while waiting for refresh after deactivating each subscription.
I suggest adding a speedy view to the admin panel: Search by customer.
The search field would take one of:
[li]an email address[/li]
[li]first and or last name (non case sensitive)[/li]
It would return important info about that person:
[li]a link to update the customer info (while they are on the phone with you)[/li]
[li]transactions (maybe ajax collapse old ones)[/li]
[li]subscriptions (both active and inactive)[/li]
My XML handling store's admin panel started out much like yours - oriented toward the database tables. Later is became obvious that we're more interested in customers than the pieces. So I added the customer search and that's mostly all that is used now by our admins.
I could probably do a mock up something like this using REST but it would only help my store/cart and not the rest of the foxy admins.
Oh and as long as I'm wishing:
I wish foxycart would check for doubling up on a subscription. We get people renewing ahead of time and creating a second sub. We had one make 4 monthly subscriptions before we caught it.