I have done it once, and yes it takes forever for the engines to spool back up (in the order of 30+ secs is probably about right). However, I did have "forever" available, as with idle thrust and speed brakes out the speed was still increasing reaching a point well into the clacker (reaching almost .85 if I remember correctly).
Still in the clacker, I increased thrust as soon as the trend vector reversed and it took a long time to spool up, but an equally long time for the speed to decrease. But if you wait with increasing thrust, until the speed is back in the normal range you might set yourself up for a problem.
I agree 100% with john_tullamarine. It was a non issue, and no need to get stressed about. Just reduce speed calmly and no reason to panic. I could have started climbing, but it went so fast that the speed was already approaching .85 and the increasing trend vector starting to become less and expected to start reversing, that I didn't find it made any sense. My thinking was it was better to let it fly straight ahead, rather than to introduce G into the equation. The whole experience was unnoticeable, no turbulence, no previous warnings, no big changes in the wind was forecasted, no nothing. MMO is just a line drawn on a piece of paper in some manual that someone had to give an approval stamp. I can attest to that a 737 flies just fine at .85, and doesn't fall out of the sky or get's bend out of shape (in order not to be sued, I will however add the disclaimer "please respect the limits set out by the Boeing, and I assume no responsibility if you exceed them either inadvertently or on purpose").
Had it been the other way around (decreasing headwind), I think it would have been a non issue, as the sheer was really smooth and gradual. I think the increase in thrust would have been much faster to hold the speed up. What I am getting at is, that the engines really spool down quite slowly too, which was contributing to the speed getting that high.
I would never let the thrust reduce to idle, for a small speed excursion, but in this case there was nothing else to do, and obviously with .85 there is a lot of time to before the speed decays to a critical level, to increase thrust again. For normal small increases in speed (like flying at .79ish having .815 and increasing trend vector), I recommend to start pulling the speed brake, before even touching the thrust levers - it usually works by itself. Due to the slow spool down time, speed brakes are much more effective (instant drag as opposed to slow decrease in thrust).
As for paperwork, it's one line in the Techlog, a 5 min inspection of the flaps and another line by the technician to sign it out again. And filling out a report, which takes 5 mins. No big deal really.