So, I do have Elite (not Atlas-Elite, only normal) but otherwise I don’t spend a penny. I am quite active though.
As you said, always save atleast Bronzechests for PvP.
For my gold chests I open most of them during PvP. However I use http://wd-orca.epizy.com/?i=1 (Orcas Chestpredictor) to see if I will get something worthwile out of my goldchests and open accordingly during other events aswell - not wasting my chests.
For the second half of the last season I didn’t spend a Bronzechest. I saved them to open them during discount now. Had 4800 Chests saved up - Got me 6300 Sigils.
Makes finishing the Discount Dragon sooo much easier.
You will also snowball a bit. Getting more sigils means finishing more lines, which leads to more stuff and more goldchests.
And with the stuff you got at the start, you can get pretty well through the season - and have a nice start for the next one!