When reading the original post I had the same thought.. $400 for partial view sounds ridiculous (because it IS..). HOWEVER, I did a quick search on Ticketmaster for March, April and May and the low end of resale for C 17 and C 19 was $376 per ticket, plus fees, so the $400 isn't too far off what has become going rate for those seats.
A quick check of StubHub and Ticketmaster for tonight shows 110 available tix, 8% of the available Richard Rodgers Inventory of 1344. with tickets ranging from $190 for Rear Mezz to $2500+ for Center Orchestra, with side Orch F 17-21 listed at $360/each.
The rate does seem to be on par with the inventory that is available in the market for those tix, I wonder how many of these seats end up empty/unsold in the end.