DB-like operations (subset, search, etc.) on multiple mail folders?

Wondering if procmail is the right tool for this.

My mail archives are eating me alive and I need a mail archive DB.  I
have read the man pages and a mail filtering FAQ and some of the
best-of archives.  I have heard of hypermail but doubt it would work.
I subscribe to this list but find it overwhelming.

These are multiple unix-style folders in 10 directories.  30MB and 500
files total.

I currently use vm.el virtual folders, dired.el with hacks, find,
grep, xargs, awk, sh, etc.  vm.el is powerful but can't handle the
volume.  The Unix tools can handle the volume but are not powerful
enough.  I don't think gnus.el 5 would be both powerful enough and
able to handle the volume.

I am open to all suggestions, especially emacs ones.

Things I want to do:

        o flag duplicate messages (Message-id: would be sufficient as
          a key) across all my ~300 folders, and ask me which
          duplicates I would like to delete.  It would be nice to
          indicate which ones VM has put certain marks such as
          "replied" on.  The messages should be deleted in-place
          without messing up vm.el, and there should be backups made.

        o make a temporary folder that consists of all messages that:

                o contain a certain keyword
                o are from a certain author
                o are from a certain author and contain a certain
                  keyword in the text
                o are from a certain author and contain a certain
                  keyword in the header
                o etc.

        o for each folder run each message through a filter program
          that returns a numeric score for that message, append a
          header in-place with the score to that message.  Optionally
          sort the entire folder by score. vm.el should work properly
          after this has been done.

        o etc.

I want something that's pretty fast and DB-like, but don't want a DB
per se.  I like the mail folders just like they are.  (I think.)

I am also interested in whether anybody has lisp or elisp front ends
to procmail, to reduce the need to make sure that one has the procmail
syntax correct.

I deem procmail to be probably the best thing out there for various
mail activities, but don't know if it can do this type of thing
without more procmail hacking than I have the time for.  I am afraid
of its syntax and the easy-to-shoot-oneself-in-the-foot aspect of it.
Of course, this is an archive, so it is safer than primary email.

Comments?