So I've done the delete folder thing numerous times, I've deleted/reinstalled the wallet programs, I've redownloaded the blockchain numerous times... And now that FINALLY both the CLI and GUI are working right, and I'm certainly logged into the wallet used for pool payments... The buggy pieces of poo wont display any balance that definitely had payments sent to it from pool.sumokoin.com

Anyone have any idea how to make past incoming transfers show up?

Blockchain definitely fully synced right now to current block 51786.
Rescanning the blockchain is your best bet (by clicking the button on the gui wallet). Do that and come back. If you ve restored your wallet properly from keys or seed words be sure that your coins are not lost.
No dice for working after trying to rescan blockchain. Still shows 0 balance. Guess those coins are considered a donation now

Everything works for successfully getting into the correct wallet (through CLI or GUI), just shows absolutely no balance.
Pls try to retrieve your seed words (at Settings tab) and restore your wallet with the seed (by select "New Wallet..." button at Settings tab)
I had tried that

, seed is accepted but then the following pop up where you enter required password doesn't work. It shoots off an error message saying "please use 6 characters long yada yada"... Even though the password works everywhere else to unlock wallet (CLI & for GUI when going the import wallet route).
When I first started out I had tried creating a wallet through GUI, rather then using CLI, and it would give that same error message when initially trying to create a password. So I tried some long password with like 10 of each characters/special characters/numbers and yet it'd still shoot off error saying not accepted as usable password.
So since that initial GUI wallet creation attempt never worked, I created the wallet through CLI and then imported into GUI.
So in other words, I think I give up

Maybe a new release will be less buggy and the coins wont be lost in the abyss.
Strange... never heard of this before. Can you report your OS? Would be nice if dev are able to remove a bug if there really is one.