This was my first time delegating SPT so I can't say for sure.

Here's what @monster-curator had to say about earnings:

      "Every 2000 SPT upvote is worth 1000 SPT for the author (and 1000 SPT for the curators). At the current price of SPS and SPT, these 1000 SPT are worth $5 in SPS airdrops and 20 HIVE when you would sell them today. Our 100% upvote is worth 7000 SPT at full voting power - reserved for the very best content!

      When you stake und curate (yourself or via us), you can earn a large amount of SPT curation rewards over the year (I don't have the current APR but it is probably higher than 30%), further increasing your SPS airdrops. You can additionally stake your earned SPS and earn staking rewards of currently 365% APR (which will go down over time as more people stake SPS)."

Hope that helps!