Kinda reminds me of a "rule" I once read on TV Tropes that claimed that the speed of female characters in anime is inversely proportional to the amount of covered skin.
@SPArcheon I found it the other way around: since the bonus upgrades have diminishing returns (due to quickly escalating prices), but multiple bonuses can interact multiplicatively, a well-fitting pair of bonuses is actually worth upgrading evenly. Forgot which pair I focused on though by now.