He's right, I have a 130spII and the media comp will vary depending on humidity and temperature if your not in a completely controlled environment.
You can even adjust the media comp as it is printing. Figure out the right comp for each material, write it down and adjust each time. It kinda sucks doing that but its the only way to ensure high quality prints.
My machine is on firmware 3.10 allowing for bulk ink and constant access to service mode from the setup menu directly. If you mess with anything, don't expect to get a good result without reading the service manual (available on the yahoo user's group) and using some magnification. There is a great little illuminated "microscope" thats available at radio shack that some of the yahoo group guys have recommended and I have been happy with it for the price.
As far as media comp goes, most manufacturers recommend that you do a quick test every time you load up media. You'll also find on really long print runs that you'll have to chase it a little.
Finally, the media comp print test is intentionally not very opaque and its very "bandy" its not a problem with your machine. It actually makes it easier to see the adjustment under magnification.
The regular users manual deals with the media comp and other non-service menu adjustments. Its worth reading. The service manual IMHO is mandatory mimaki reading.