any way to speed up dpkg-scanpackages?

[Tom <tb.31112.nospam@comcast.net>]

I have 727 .debs in a directory as my "local cache".  Whenever the 
contents of the directory changes, I dpkg-scanpackages to find the dups 
and write the Packages file.  It takes many seconds to complete.

Since the directory changes little each time, it seems like lots of the 
work must be wasted.  It reminds me of a moderately sized SQL table 
without an index.  Is there any way to "Index" the debs, or reuse the 
mostly still-good Packages file, so that dpkg-scanpackage is faster?

(This is an architectural question.)