I think the price on statues should be cut in half then. You basically made all SR not persuadable and the R+ that are persuadable are not that good. I might as well take my chances with a gold rescue, which currently will cost me less.
Half is a very reasonable price so I would strongly support this suggestion.
Even for this Succubus Dungeon event, the special Rescue (Tidal Wave, was it? Can't remember from the top of my head) guaranteed a R+, for 300 gold.
It seems that on this game, people who may spend a small amount of money doesn't really have that much of an advantage over the players who may not spend any money at all.
On the other hand, if you're the person who may spend hundreds of dollars on this game, you might as well could fill up your attack crew with Maxed Athenas and get first place in most of the events.
The above is rather unbalanced, if you ask me...