For future reference, you might like to know that there are now regular payment gateway/merchant account combinations where you can use their systems to handle the final part of the transaction so you never even have card numbers on your network, so the PCI DSS issues are moot, at least here in the UK. The lock-in isn't ideal, but as far as I know only Recurly out of the major billing services doesn't effectively lock you in just as badly anyway.
However, we've found that the recurring billing platforms tend to lack precisely the kind of flexibility you mentioned above. We have all kinds of plans to use promotional codes, multiple offerings that users can subscribe to individually or in combination, etc. As far as we can tell, none of the "big name" billing services even gets close to supporting this kind of stuff properly yet.
For the benefit of anyone else following this discussion, I'll also mention that because we're in the UK but most (all?) of those billing services are across the Atlantic, there are serious concerns about legal differences, particularly data protection/privacy rules, and about tax, particularly how VAT is handled. Again, the billing services whose terms and conditions we've checked out had deal-breakers here.
Given that the billing services take a relatively large cut out of the payments, sometimes with terms that don't even guarantee any particular level of service, and that we'd have to implement a whole bunch of things on top of their platform anyway, we concluded that they simply don't offer enough to justify the risks and overheads.