Rank (or grade) in judo should be a reflection of knowledge and skill. For sub kodansha rank (ie 4 dan and below) and the first kodansha rank itself (5 dan) the emphasis should be on skill which in part translates to contest (not championship) success.
For those kodansha ranks that come with a kohaku obi (ie 6 to 8 dan) there should be a greater emphasis on knowledge as by the time one is at this level, one's physical capabilities are in decline, through age. There should also perhaps be a component of contribution or service to judo - through teaching, research and publication, administration or other leadership. Moreover, as ranks are personal to the individual, knowledge should be the overwhelming criteria. It would also say that judoka at these ranks still have to strive to continuously better themselves and that they should not receive further promotions merely for continuing to live and for the same achievement over and over again.
However, in most areas of the world, "service to judo" has actually come to mean "service to judo governing bodies" or "service to a particular judo politician". In most areas, organisational leadership of national, continental and international bodies is now in the hand of the judo politicians or "committee-men", and they use rank promotions, particularly the awarding or witholding of kohaku ones to reward the faithful, punish the dissident and also as a means of controlling the behaviour and attitude of many other judoka who are hopeful of reciving such a promotion sometime in the future. I have seen many instances where supporting the political agenda, not speaking out against the party line, attending "political meetings" and helping the judo politicians, results in promotion. I have also seen instances where those who have taken a different course have had their promotions continuously blocked.
As for promotions to high kodansha - 9 and 10 dan, they clearly mean different things in Japan and elsewhere. Time in grade (as an active 8 dan) for promotion to 9 dan is about 21 years - though Uemura-kancho has been fast tracked. Even in Japan 9 dan promotion is politicised with the majority going to those judoka associated with the Kodokan or resident in the Tokyo area. In the West 9 and 10 dan promotions have, with a few exceptions, gone to the uber-judo-politicians with high levels of service to the IJF and Continental bodies through administration, committee membership and refereeing. Some of these people have very strong contest records in their early career, some do not. What I feel is needed for these ranks is a very strong foundation of knowledge, coupled with some exceptional achievements in some aspect of judo.