I've thought of some mechanisms to make the liking system m…

I've thought of some mechanisms to make the liking system more transparent, which I will implement later. This won't limit your ability to give likes to Ordinals multiple times if you enjoy it to expensive items, maybe if someone can't afford to buy it. You can even purchase an ordinal and continue sending rewards to the creator through micro-payments for likes.
I think it's a good idea to have a ranking based on unique likes. As you may have noticed, there are many ranking categories so that no one can monopolize them all.
Limiting the system to prevent self-liking isn't the solution because someone could simply create multiple accounts. Today, the visibility of relevant content in social networks is distorted by bot farms, since likes, follows, and replies are free. However, spam is partially mitigated when it has an economic cost, not just a computational one.