Unless you totally rely on bookings as your source of income, I'd stay away from the instant book. You basically answered your own question- "particular about who I allow to stay" and"that is how I ensure good guests who do not destoy my home". I feel and operate exactly the same.
I think it's a mistake to assume that bookings have dropped off because of something you are or aren't doing. I'm getting less this season as well and have 5 star superhost and all great reviews. Might just be the economy- people not being able to afford to vacation right now.
And remember- airbnb does not have very good host support (maybe an understatement?) in cases of damage claims and other issues- they almost always side with the guest. Do you want to be steady booked with guests who you haven't had an opportunity to get a read on, or less booked with guests you've had the chance to vet first?