My theory is that you can maybe create a math formula, that helps calculating, when delegation can potentially mean more ROI than the "opportunity cost". (e.g. delegating to @smartsteem or @minnowbooster instead)

Of course it has many uncertain, and as such, probability factors, like SteemUA acc voting power/weight fluctuation over time, or UA fluctuation itself, but considering on my own example that an UA of 2 can bring you to the top 25k (at least!) among a million users overall (top 2.5%) (even on 50k daily active users, it's likely a top 50%), I'd say that every delegation above 25SP from an account with >2UA very likely has a higher ROI than not delegating.

@paulag or someone else good at math may do a calculation on it.