I saw here, how high-ranking members would be the first to get included in the best signature campaigns. I would feel frustrated as a newbie as I felt irrelevant and ignored as my rank was not that good so was my reputation.
Some campaigns give participants same pay rates from Senior Member to Hero, Legendary member ranks so ranks mean more for below Senior member ranks and in general, there is nearly no difference between Hero member rank and Legendary rank in most campaigns.
Many reasons to want ranking up like have a higher rank badge, more coins on the badge, the rank title. Chance to wear bigger signature with bigger limitation on maximum characters in the signature space. It is cool feeling when I wear a signature for Senior member rank than for Full member rank.