I am working on Wisdom title track so need the golds badly.... I started to keep a record of which chests my 7 characters have opened, and (lately) the last date they opened.
The first time I 'revisited' a chest was 13th March, and it was one that I hadn't opened for a couple of months. That day I was able to get 4-5 golds from re-opening with 1-2 characters. I am just talking about the chests in Istan and Kourna now that all my Prophecies and Factions characters can access with minimal NF advancement.
Anyway so I left it to 18th April and thought "it's about a month now" so started to revisit these four chests again with the same characters that opened them on 13th March. Character #1 got 4 golds. Character #2 got 2 golds from the first couple then empty from the second couple (despite having last opened them all on the same day). Characters #3 and #4 got all empty from all four chests straight after this - this was their first 'revisit' and again they had last opened these on 13th March, same as Character #1. So instead of 16 golds I got 6 from the first 6, then 10 empties straight after.
This is leading me to interpret that there is some kind of account-based limitation - possibly even anti-farm. A guildie who is with me disputes this hotly. He was accompanying me on some of these trips, having opened chests for maybe the 3rd or 4th time, and getting purples (and really quite surprised and annoyed by this

). His theory is that everything is character-based but, sorry, this doesn't work for me.
If I go to the same 4 chests/same date-interval across 4 characters and get
Gold, Gold, Gold, Gold, Gold, Gold, Empty x10
....in that order, this does not look like a random sequence. There has to be something account-based.
What I am therefore also wondering is therefore whether repeated opening of the Istani and Kournan chests will jeopardise re-opening of the ones in high-end areas.
Anyhow...I am not expecting anything more than a single drop from these chests and was delighted they re-open at all. Re-opening too often would only pump too much cash into the game economy anyway and I am sure A-Net would want to put something in place to stop people farming them systematically. The only reason I did this is - as I say - to get golds for ID as 10,000 is rather a lot to max a title (and I refuse to buy them in trading centers).
I'd be interested to know people's theories on what is the minimum/best interval to re-open, what determines gold/purple output, and whether there is a limitation either at character or account level.
If there is already a thread somewhere on this - my apologies - please can someone provide a link. Cheers.