Usually, worn out springs are very soft. Yes, the springs will continue to sag over time, the more worn they get, the quicker they will degrade and eventually you'll end up with a broken leaf in the pack. Especially once they start to sag lower than the center where the block is, yours are not there yet thankfully.
So a new set of springs will ride "firmer". Whether it's an improvement or not is completely subjective. But it will not soften or smooth the ride, that is guaranteed. I like a firmer ride, some of my friends want their truck to ride like a couch on wheels (like a Cadillac). You might be able to talk to a spring company that can put you together a spring pack that is softer than stock but will be arched correctly to be able to get rid of that block, though I'm not sure what that would entail on your end for measurements.