I know Selective spell would negate the need for saves against the fascination effect, but there's more to it. I need to assess the tactical value of this combo.
Question 1: Do all creatures I select with Selective Spell HAVE to be within the spells effect at time of creation? I'm assuming yes, but just making sure.
Question 2: Do selected creatures get to ignore the visual impairment (Miss chance, blocked vision) caused by the spell? Say, could an archer target creatures inside or on the other side normally without having to worry about the normal rules for areas of fog? "These targets are excluded from the effects of your spell." seems to indicate that any impairment can be ignored as if the spell didn't exist.
You are operating under an incorrect assumption...
You can not use Selective Spell metamagic on that particular spell.
When casting a selective spell with an area effect and a duration of instantaneous, you can choose a number of targets in the area equal to the ability score modifier used to determine bonus spells of the same type (Charisma for bards, oracles, paladins, sorcerers, and summoners; Intelligence for witches and wizards; Wisdom for clerics, druids, inquisitors, and rangers). These targets are excluded from the effects of your spell. A selective spell uses up a spell slot one level higher than the spell's actual level.
Relevant portion bolded.