Okay, doing some more experimenting I'm still getting a bit of a mixed bag, but at least now I'm getting mostly positive results by NOT pushing the games down.
It still seems very fiddly and even a slight bump can still cause some graphic corruption... wondering if I have a pin or two that just aren't making very good connections period.
The plus side? A game I had written off as being completely dead (High Speed) is working using this method. How I'm not even sure... the game was bought used a decade ago... when I opened it up, it had apparent water damage (or was left by a window in a salty beach hotel). Besides the contacts being heavily corroded, there was corrosion on the PCB itself... Even at the best of times we often only got the game to work before with graphic issues.
Managed to get the game to not only load up, but looking perfect.
So long story short, I'll likely need to fluff the pins, but it's looking good.
A new issue though... The fact that pushing down the game is causing issues (and could lead to future pin issues) I need to find a way to disable the pushing down mechanism. Why? One of the reasons I wanted to get the NES working is for my autistic elder brother. He's very low functioning (high motor function, but low cognitive/intelligence levels). One of his favorite things was playing the NES. He's loving that the system works, but part of his autism is having extremely strong OCD. He knows he's "supposed" to push the cart down... and while he'll listen to me when I'm over his shoulder reminding him, when he works the system himself he reverts back (and gets frustrated and sometimes even mildly violent when the game doesn't work)
I've ordered a cheap-o $15 knock off NES that'll be here in a few days that I HOPE will work well enough to play his favorite games and I'll reclaim the NES myself (having worked on it so much lately, I've started to become VERY attached to it again). That said, if the system doesn't work well enough for him (I plan on letting him have one of the refurbished original NES controllers so quality of that is a non-issue) I'll bite the bullet and take the knock off.
So yeah, anyone have any ideas for a simple way to lock the tray upright?