How to get out of a provisioning/signing/certificate mess?

I have published an app on the AppStore. I haven't needed to update it since January '13. But all profiles/certificates/etc. expired and I've probably made things worse trying to fix it. My version of Xcode is older (4.5.2) and I'm terrified to upgrade because last time it caused huge problems. I'm targeting iOS 4.3 (lowest common denominator) which is hard to do with newer versions of Xcode.

The current issue is in signing when I try to build for a Device.

There also seems to be this awful bug (IMO) in Xcode where it keeps caching old certs, so they keep appearing when I try to delete them (thanks StackOverflow for cluing me in to that).
I'm not sure what should be done via Xcode and what should be done via Member Center...they don't seem to interact very well (errors when I try to refresh in Xcode, etc.).
I'm afraid to delete everything because I'm afraid it won't let me update my app if something's changed (like the application-identifier) and I'll have to re-publish under a different name?! Other things seem impossible to delete.

So for starters-- is there anything I *shouldn't* delete if I'm worried about not being able to update my app? Is there anything I won't be able to delete? Any other tips for how to start over with a huge provisioning/signing/certificate mess, such that I can continue to use Xcode 4.5.2 and update my app?

Thanks in advance.