Yeah I'm pretty sure there is no strain. Also the darkside already kinda sorta manifest as long term conscequences. You roll Morality at the end of the adventure. Thus there is a chance you can gain points that would nuetralize that one bad act. That's pretty tempting, as when you make use of the darkside there isn't always going to be a bad thing that happens. Also I find failing if you don't take that darkside pip pretty tempting.
I think the Force would be less fun if I had to wait a turn or two before the power kicked in. The current rules already do a good job of depicting the slide I feel. With the up and down way that Morality can bounce back and forth, one bad action, a series of bad actions, you never know what will push you over that edge.
I know the long term consequences are already there, which was kind of my point: if you put in short term AND long term penalties for using the dark side, it kind of goes against the way it works in the universe, which is short term gains but long-term degradation. My point is that using the darkside is rarely tempting from a player standpoint not because of the Conflict generated, but because of the immediate consequences in suffering Strain and flipping a DP. Giving the option to "give in" to the Dark side and remove those penalties in return for more Conflict gained is my attempt at giving the "seductive" dark side option for players.