Look at it like this. Look at it like this.
Heads are the single biggest area to gain power in a stock smog era small block.
You can make 100 extra horsepower with the heads you have by putting in a bigger cam,intake and headers,but the motor would need to be more radical to get the power. With a good set of heads you can make that extra 100 horsepower without as lumpy of a cam or the associated headaches that go with it. You can cram a big cam and reconfigure your combo to work with the increased rpm or buy beter heads and maybe have the power you want at an rpm range that matches your current combo. You can bolt a set of 64cc dart sportsman 2's onto an otherwise good running low compression 350 chevy and pick up a little compression and about 50 horsepower without changing anything else,that is 50 horsepower that doesnt idle rough or get bad gas mileage. You can make 100 extra horsepower with the heads you have by putting in a bigger cam,intake and headers,but the motor would need to be more radical to get the power.