Zip should be applied to EVERYTHING that goes up there.
Example of A/B comparison: from
http://www.jdlx-musique.com/support/an1x/downloads.htm, the file Pavage8 has
a compression ration of 92%! Before - 221kb, after 17.7kb.
Regarding obsolete Zip formats: Try
http://www.simtel.net and search for
older versions.
The present version of Zip has been out for over 5 years, Phil Katz probably
isn't gonna mess with the algorithm soon (Phil Katz, inventor of PKZIP, is a
millionaire now due to his shareware program pkzip released in the late
80s.)
The only files that shouldn't be zipped are formats that are compression
formats to start with such as .jpg, .jif and .pdf. Otherwize, there are
redundancies in most files that Zip can compress.