Right, that’s my point though. With my '84 Chevy Monte Carlo SS, I could drop a new engine in (started with a 305, ended with a 400 short block), do a high-flow dual carb intake, get a couple Edelbrock carbs, buy some headers, straight pipes and a glasspack muffler, and get a ton more power. (And also much, much worse fuel economy.)

Right. But with a lot of modern cars, you don't need to drop in a new engine at all, and for a lot of people changing fuel trim tables is easier than getting carb jets juuuuuust right. Not to mention there are premade stage1 remaps for stock engines that should "mostly" work. There are engines out there that will give you around a 30% without a single mod, though generally not on those premade remaps, as those try to err on the safe side. Stock intake, stock exhaust, stock everything. Just a remap. Oftentimes, they give you BETTER fuel economy because of the improved torque curve. Though the increased effect of the fun pedal often cancels this out.

I'd say you can get into modding with less knowledge and skill nowadays, because as long as you have the hardware, you can get someone to remap your car remotely so you don't even need to be able to drive it to a shop after doing whatever mods you want to do to it. True, if you want to do everything by yourself, then it's harder.