As I think about it, if all you want is that one Temple Garden, then selling the other two as a sort-of-rebate might be pretty good. As far as we know the enemy shocks will have half the the supply, and the Bant box has two U/x lands and one of them is Breeding Pool which I do think will hold a decent price. You still have some time to see how things move. Full disclosure, I like secret lair more than dislike; the ones that don't look like magic cards really appeal to me like the band posters and heavy metal.
Tough call. Certainly the price will drop some once supply starts getting into people's hands, but it will go back up; where it settles is hard to predict. You could always buy the SL and plan to sell the other two lands as a form of rebate if you really just want that one land.
Fractured Identity is a decent value too which surprised me when I saw it.