In general, the metadata of a Revision remains the same, only the electronic object changes. In that case, the Last Action Date is updated to reflect that, in addition to any other logging you may have turned on.
If you wish to have the metadata change with each new electronic object, then you could look into Versions. That feature allows for the metadata to be searchable on each Version while relating the records together for reference.
Another workaround option would be to utilize the Comments section when Checking In an electronic document as a Revision. The Comments entered go into the Notes field, which is searchable.
As a last option you can use the Online Audit Log. I've got a script that searches through all audit entries (title changes, etc) so that you can effectively execute an eDiscovery against TRIM. Unfortunately you can't do that directly through the UI though.