A wordplay idea: could it be
ICE?
I make many feel like mice.
Turn anything into ice and "many" becomes "mice".
Some think I'm the open.
The Open as in golf - you can play ice golf.
But sometimes I am nice,
A common mishearing: e.g. if your ship is stuck in pack ice and you see a gigantic beast approaching you across the floes, you really want to know whether it's saying "I'm a nice monster" or just "I'm an ice monster."
No need for doping.
???
You'll see what I am after,
Maybe you'll even say "Yay!"
Well, if you solve the riddle to find what the OP is after, "Yay!" is certainly an appropriate response.
I rarely hear laughter,
No matter what the day.
A common metaphor: if someone has an icy demeanour, they won't laugh much.
Half of this is crucial,
The other not so much.
Half of the word "this" is "is", which is similar to "ice".
This puzzle may be social,
Well, it's certainly attracted a lot of answers (and probably got on the HNQs)!
Let's see who's super clutch.
I've no idea what this means.
Disclaimer: I haven't read all the OP's comments on other answers (though I have checked that nobody's already posted this as an answer), so apologies if I'm trying something that's already been excluded.