I don't care about my EP any more, because I've got to a point where there aren't really any rewards that I actually care about within an easily achievable range, so is there actually any point in wasting my focus on Toriumi Hinata, or should I just elixir her/wait for her to go away while hoping that a PeroFriend finds Sera Hoshizaki?

If it makes any difference I'm F2P.

Well, if you have the peropero to spare on buying extra elixers: why not? You can spend your focus points only once, they make a bigger limitation on how often you can fight either EG or SEG than your stamina, and those SEG rewards are probably easier to reach if you and your friends manage to spawn enough of them, while they still give you EP anyway, so you might still get some of the EP rewards on the side.

well they drop a lot of wild card so i usually do 1 weak att and let my ally kill them