Lunar+ was released December 4th, 2021. That was 33 months ago. The highest milestone takes 42 months to achieve. This means that even if you started buying Lunar+ from release, you wouldn't even have the maximum reward. Also, if you break the streak, you have to restart.
My proposal is to make Lunar+ colors called Plus Colors. You would unlock Plus Colors by spending a certain amount of money in the Lunar store. There would be a minimum of some amount that makes it so not everybody is running around with a +, maybe $100 or so. I think having cash milestones instead of tri-monthly milestones is a much better, more user friendly way to reward Lunar Client spenders.
The pink logo would still be exclusive to Lunar+ users.