I still have 2000 HP leased to me at no cost and it's been almost a year I think. I guess the trick is to have multiple smaller leases and hope some of them don't get canceled. The fact that you have higher HP usually also means you'll get more upvotes on your posts which compensate for the slight loss in curation. Overall if you are active on hive and below a certain range below 50-100k HP, I guess it's always +EV to delegate. Once higher it likely won't lead to more as it gets exponentially harder to get more upvotes once your posts already do reasonably well.
good luck!