I am not familiar with gifresize, but I vaguely recall seeing some old
references to GIF software removing the LZW compression, due to Unisys
patent claims.  That may be what you are seeing.  What were the
dimensions of the image after resizing?  (If you multiply the width
times the height, do you get anything close to the size of 24570 byte
filesize you wound up with?  (^&)

There are lots of better formats that GIF:

 IFF: Made GIF obsolete before GIF was even created.  (^&  Not
      widely used, and does not compress as well.
 PNG: The Unisys patents were the reason that PNG was created.
      It does paletted images as well as RGB.  It has a better
      compression algorithm (LZ77) which can be implemented without
      infringing on any known patents.  PNG is also "almost" an IFF
      format...
 PNM: Kind of the antithesis of efficient, but if you bzip2 the files
      they can get significantly smaller than PNG, if disk space is your
      thing.  It's also extremely easy to decode.
 TIFF:Maybe a better archival format than PNM; I don't think that it
      supports compression any better than PNM, but like PNM can be
      externally compressed.
 JPEG:If you're willing to accept some lost details, the space savings
      of JPEG may be worthwhile.


-- 
  "I probably don't know what I'm talking about."  http://www.olib.org/~rkr/