What enemy sites? Most of the galaxy is empty and you can explore stuff exactly one time anyway, so if you constrain power play exploration to power play alone you'd run out of enemy systems to scan pretty fast, even if every single system outside of your power's sphere of influence counts as enemy site.
Really, it would make more sense to give out merits to explorers coming home based on discoveries. Also the merit-decay just doesn't work if you're making month long trips all the time, like most explorers do. So merit-decay would have to switch off or something if you're far away enough from civilized space. Essentially, power play as it is now is one giant handicap for explorers. Explorers face a binary choice: Either participate in power play or go out exploring, but not both.
