I struggle to think of a scenario.
Trading out from top two means increased risk on ceilings.
Trading for someone who is in the same talent range, means you're either acquiring an established player who has proven their abilities (and thus will be coming in at a higher price point), or you're acquiring a guy who has some question marks.
One of the big reasons players like Hughes/Kakko are coveted is because of the talent/cost crossover.
Forget what they might be in their primes, you're potentially getting some very good production at a lower price point than if you paid a veteran player.
For example, let's say Kakko scores 20 goals and 40 points next season, 25/50 the next year, and 25/60 the year after.
For a very reasonable contract, you just netted 70 goals and 150 points over a three year span. Even the next contract isn't as likely to match the cost of having to go out and bid for talent at that level. Alternatively, that next contract brings with it the possibility of costing you more over the short-term, but providing a significant discount over a longer period of time.
So in addition to talent, there's the ROI to consider. Generally speaking, those young elite talents provide a significant cost savings compared to older, but similar production.