Do you have an EX raid pass? If not, then no reason at all. If so, I would wait until you are at the raid and the egg hatches and you do a probing run to see whether it has Focus Blast or Hyper Beam. There is also small speculation now that the next round of EX raids will be Ho-Oh, in which you really don't need to power up Gengar.
GamePress
Non-legacy Gengar
I already have a 89 ivs SC/ ShB Gengar (15 atk iv) at level 38, it’s my only powered up Gengar and also my only one legacy one, however at soloing FB Zam or battling Mewtwo with that move people say that Gengar rocks, I have a 98 ivs (15 15 14) one with Hex/ ShB and tons of candies, it is worth to invest?
