Hello good gardening people.
I've got my Peace Lily (Spathiphyllum) in a South Australian office and I'm afraid it will continue to decline and die.
I water it when a finger in the soil is not properly moist and blame the ducted air conditioning for its struggles. The soil is never completely dry to the touch, do you think I could over over/underwatering it or my finger test is fine?
Most leaves are entirely green (except a few with dark splotching) but its down to one healthy flower, with three wilting yellow and two look malformed.
I just removed about 5 dried out brown flowers that were beyond salvaging.

When I first brought it in the office I read direct sunlight was bad, so I moved it away from the large window wall (that seems to be tinted by something). I'm tempted to move it back into direct sunlight, perhaps the tinting would make this ok?
I read over fertilizing it could be an issue and have not fertilized it. Should I? How?
I read air conditioning should be combated by spraying the plant. I haven't got my hands of a spray bottle but I just moistened the leaves with a damp tissue for the first time. Should I keep this up?

What else should I try to get this to be a happy, vibrant and healthy plant?

Peace Lily flowers rarely last longer than a week or two, so their demise does not mean your plant is unhappy. Cut off the flower stems as soon as the flowers start to fade.

Your watering is probably about right. Ideally, you should water a Peace Lily just as or before it starts to wilt. An occasional wilt from dryness will not harm the plant. Water it really thoroughly and then see how long it goes before it starts to wilt. That will tell you how often it needs water. This is a plant that doesn't tolerate dry soil, although it can be overwatered.

Very bright light that avoids the rays of the sun falling directly on the leaves is best. Peace Lilies also do well under just office fluorescent lights if the lights are on for at least 8 hours every workday.

Monthly fertilizer at half strength will help promote flowering,

Unless the AC is very close to and blowing directly on the foliage, it should not be a problem. Misting will not help with either the AC or low humidity. Do it if it makes you feel better, otherwise, don't bother.