I don't have anything against collector raids and agree that walls are expensive. However I often see people who only raid collectors that are unable to get BK to 10 and get their dark troops finished at TH8. So imho try to balance it out so you can keep your dark upgrades inline with your wall upgrades. If you can do this only with BAM or barch that's great but I found the need to hit storages when i was going after dark.
One way to mix these storage raids in is to train them when you are planning on signing off for a while.
I'm at around 1500/1600 cups (I try to keep Gold 2 badge so bonus is slightly higher) and there are quite a lot of dead bases.
I tried Silver because I was there at TH7 but I was finding literally nothing
Didn't go any higher than Gold 2 because really it's just more than fine
I didn't read the thread, so excuse my reply if it's just repeating what has already been said...
Silver 3 and below. That's where I farm for all town hall levels. I find plenty down there. Patience.
Theres lot of dead bases in crystal about 2000-2400
Im having no problem with this I think if your not there already you should drop to gold 3 there's plenty over there it rarely takes more than 5 minutes to find a 400k to800k raid