Yes and no. In terms of picking up retro cheap, that horse has bolted years ago. Folks who look for high value items to resell travel to car boots and either ask sellers while they're waiting to get in or try to get there first etc. etc. - they're pretty thorough, and video games have now joined the list of things they ask for like "gold, fishing tackle, perfume". Charity shops etc. increasingly hoard gaming related items like they're priceless jewels etc. etc. (even if they're worthless crap nobody wants). That's not to say you'll never find any, some always slip through the cracks, but if the object of of your buying trip is to find retro games cheap then most of the time you'll be disappointed.
Last-gen stuff is cheap to collect and always at that sweet-spot, everyone's dumping the stuff and the hard to find ones are mixed in, so time to grab them before they disappear and start to rise in price after so many years. I watched a Metal Jesus Rocks video the other day and he suggested "when everyone's going one way, you go the other", and that's exactly it, don't collect what's in, collect what's out, you'll get multiples of games for the same money. The 360/PS3 have a wealth of brilliant games, with much less spread than can be found on the PS4/PS2 in terms of genres, but there's lots of Triple-A games and a few oddities too.
Not only do I pick up what's 'out', the way I get what I want for the right price is via trading - not with other collectors (though that's a very viable option) but by using exchange shops and retro specialists. This way I don't even need to find retro games (or even games), if it's something a store I know will take in exchange then it's credit waiting to happen. If you like to visit car boots, charity shops/goodwill, swap meets etc. etc. then learning where you can get credit for what will allow you to multiply your money.