so, quick run down.

with the car at idle and no AC, 14v.
idle 1-2 bars of AC, just under 14v
with 3-5 bars of AC, 13v
full AC, just over 12v

sometimes, itll drop below 12 for a bit, like almost to 11v. it gets really bad with the lights on at night. sometimes its right at 12v, and the car idles at 1k for minutes? as long as im at a light i guess.

its not 100% of the time, but it seems to be more and more of a thing.

car has over 99k miles now. reckon the alternators going to shyte? anyone done one before? looks like a super pita.

 

I bet at rpm when driving it is likely OK....
IMO run it....
Unless you are running big driving lights and a big amp you will never notice it...for a lot more miles....no reason to get a "new" $600 denso alternator (most aftermarket is junk) when you are not (yet) seeing any ill effects....
Folks sometimes get OCD with their mini's, but remember, as they get older, if you check most anything, it will test worn...even if it still works.

 

Mine took a dump at 80k, but it was the bearing in the back of the case that turned canibal. As for the work involved to replace it, well it depends on how you do it. No idea how long it takes if you do it using the service mode method.

Personally, when I have to work on the front of the engine, I just pull the front off and depending on the job, removing the upper rad hose and getting it out of the way (when I did the crank sensor seal) or removing it completely (when I did the A/C delete pulley and alternator). I have spare oem antifreeze, so losing some in the process isn't a problem. I'm used to take the front off, so it's a matter of not even an hour to replace an alternator if you know where you're going.