There is a built-in mechanism in Mastodon's server software which reduces how often you see the same post boosted again and again.
If you have seen a post boosted, boosts of the same post are automatically hidden from you until 80 other posts have passed through your timeline.
This mechanism previously allowed boosts to repeat after 40 other posts. The developers recently doubled this to 80 other posts, so repeated boosts should be much rarer now.
@FediTips maybe it would be nice, if this number was configurable?