Since I started ranking up in Star Planet back when it was released in GMS, I've been disappointed that previous rank rewards are not maintained. For instance, Star Planet Action Skill only retains the action of the last achieved rank. This seems odd since the normal Action Skill stores all learned actions. The only way to regain the lower tier actions is by letting yourself fall back in the ranking, and then only play enough to hold the rank and not level it up. This seems unfair to those who worked hard to achieve a higher rank. You can also consider that minigame customization rewards are kept at higher ranks, which is another reason I find it odd other parts such as the actions of Star Planet Action Skill are not. I believe previous ranks of actions should be kept when achieving a higher rank.
I will not comment on mounts because, as you know, there are medals and achievements for having a larger sum of mounts. Keeping every mount could be an issue, so I would understand keeping it to the last rank's mount. However, again, I believe Star Planet Action Skill should keep the actions of lower ranks. If I'm forgetting other parts which could logically be maintained, feel free to comment.
Note: Just to be clear, this isn't about keeping actions after losing your rank - this is about keeping the actions you get from lower ranks once you have a higher rank. Just in case anyone is confused by what I mean by variations of 'keep action skill.'