I've done it a few times, and frankly, it isn't that much of a stretch to have 2 good, quality efforts -- one doesn't have to be sacrificed for the other. I've found weather differences between the 2 events having more of an impact than the previous race.

Think of it this in this light....on a normal run-up to a goal HM, you'd have a few lighter days post race and then probably drop back into your training routine by day 4 or 5 (at most).  Certainly by week 2, you'd have a longer run or even a long tempo back into your schedule -- the second half is just replacing that long or tempo workout.

Personally, as a middle-aged hobby jogger, I can't hammer out 2 equal high effort HM on back-to-back weekends, I need to dial one back -- and for me, I get better results by running the first one at 80-90% effort, and then have the second one be the harder.  IE...easy -> hard works better than hard --> easy.

MTA:  Just checked through my log and it looks like I did 2 or 1 week back-to-back HM 4 times last year. Usually (not always), the second was the better quality result.

I'm in the midst of two half marathons 13 days apart (on day 6 of 13 today).  I raced the first pretty hard and felt like I was back to full strength just a day or two after.   Was able to have a pretty good 17 mile effort today.  So, IMHO I think you could probably go full out for both.