A autospawner with a max enbiggened (green normal) slime (spawn exact=true) seems to provide quite a net increase. And DW20 did demonstrate that autospawner with random spawning slimes that get enbiggened gives him plenty of essence to play with. Mind you, he's using 4 vet stations ^^* Ofcourse, soul-shard's with slimes -> grinder are the easiest way to get a high amount of essence ^^*
How many slime to max out a soulshard? I got luck and the first quarry I make to bedrock was a slime chunk.