there is more to it. i have been slowly investigating the methods miis can travel to the parade with help from another forums user since the launch.
miis travel to/from contacts in the address book, but i've found that a person with few miis will get 'accellerated' trevel miis compared to a person with an already large parade, regardless of the amount of contacts in address book. miis set as 'favourite' seem more likely to travel than non-fav miis. also, miis seem more likely to travel when at least 1 wii message has been sent between contacts.
'local' miis can also join the parade. that's miis from your area. the area is not known. could be city, state, console region, country etc. this was tested with a brand new wii, left with wiiconnect ON for 1 week. no messages sent/recieved, no wiis in address book, and no miis created in mii channel. about 10 miis in parade after 6 days. it may or may not matter but there was 1 other launch wii in the same room, same WLAN
nintendo can send [celebrity] miis as has happened in japan, however these 'special' miis cannot be copied, only transferred
miis can be sent directly to parade using blank wii messages with the mii as the message 'icon'
for the record the parade on my launch wii is currently over 1700 and growing 1-5 per day. 4 empty contact spaces in the address book
using the methods above i've had parades over 2200, so the limit is still unknown, and may be dependant on the wii's free internal memory
