I was about to suggest this one too! I just finished the second book and am really enjoying the series so far.
A few good Famicom/NES finds
Went to a flea market and a few retro stores I hadn't been to before up in Michigan and walked away with a few solid new games to add to my collection! I paid $100 for Lone Ranger+Best of the Best Karate and $40 for Lagrange Point. Not the crazy deals I used to see, but still pretty happy!
Btw, I'm just treating Lemmy like I used to treat /r/gamecollecting. Let me know if posting "finds" here is annoying.
I can't say I've ever found a gem when I wasn't looking for games at all, but I have found some when I wasn't expecting anything exciting.
Probably 10 years ago, I was in a kind've sketchy store in a flea market near Baltimore and found a booth piled up with old electronics and games. Was not a very nice looking place and had bootleg GBA games in a glass display case and a table of more modern games up front. I dug around in the back of the store and in one pile of wires and controllers spotted a loose copy of Dragon Warrior IV for the NES! The lady manning the booth didn't know/care what it was and sold it to me for $1. One of my favorite finds!
I also later found a boxed copy of FFV GBA (not bootleg) and a CIB Paper Mario Thousand Year Door there. Not sure what I paid for those (probably $10 a piece or something).
I've been huge on collecting NES lately. It was the first system I ever played, so I guess it has that nostalgia factor for me. I'm at 392 games so far, not sure I'll ever hit a full set but it's fun to slowly head that way. I miss being able to find random games cheap at yard sales, flea markets, etc. Wouldn't be such an easy system to collect for now!
In more recent years I've also branched out into Famicom and Famicom Disk System games. You don't see them often in the US, but it's really exciting when you do! I actually just grabbed a complete FDS Kid Icarus a couple of days ago from a local game store.