I didn't notice much if any difference in ride (softness/stiffness) in the front when I fitted mine. They have progressive rate springs which means they work harder when the bike's being pushed harder. Most obvious change in mine was that there was no more wallowing in corners and less dive under heavy brakes. Improved handling quite a bit. I should say I also swapped my tired old Standard shocks for almost new Roadster shocks at the same time which did also improve handling and gave a softer ride.
With the fork springs, I wouldn't say the improvement justifies swapping them out on their own. There are perhaps better, more expensive options if you're looking for that killer mod. However, if you're doing fork seals or servicing the forks for some other reason, you may as well swap the springs out at the same time. The Progressive springs aren't expensive and they are an improvement. Just my opinion, mind.