I’m considering trying out IS 4x for the first time. I tried looking at other forum posts, couldn’t find many info on it. I associate IS in general with happiness with self effects but also putting others in a good mood. If I were to try 4x, could I reach a wider audience or would that wear down the effect of it?
Nope - Sometimes its just right! 
Its a good economy measure really - If you are regularly using 4 sprays or more in your mixes, then its perfectly suited to cut down the amount of product/scent.
Then there are those strange nights when a megadose seems useful but if you do, prepare for the crash to hit hard if it does!
Personally, I keep IS in 2x and 4x for this reason - I seldom need just one spray!
As Mobo on this, havent OD on Shine really only issue can be covering the scent and as Mobo says self effects can become a little too much.
If you are going to do large doses then I would definetly take some days of now and again. I become very lethargic after a few on it (which great for regenerative sleep 
)
Another thing - Not so much with IO or IS but 4x IH is another product that comes into a class of its own for simple but highly effective mixes - 1-3 sprays 4xIH, with a little P75 or just some TUTH is a superb “I want to get lost in you” mix!
The popularity of hard-hitting/mindbending mixes like this has declined since the price of 4x IH went through the roof, which is a shame! 
Why is instant honesty so expensive?
Please… Not… This… One.. All… Over… Again…!