I added vogtland lowering springs to my 2009 997S can and the ride is quite a bit harsher on my beautiful Michigan roads.

After 1000 miles the drivers side front strut blew a leak with only 8000 miles on the car so I had the front struts replaced with beilstien struts.

Is the stiffness due to the spring rate or sitting deeper into the struts dampening?

It's a little late now but I've noticed coil over kit starting at $840 on up to $4000.

It is just used as a summer daily driver.

Thanks for any advice in advance.

i would say its a combination of both the stiffer springs and more compressed struts. the bilstein struts should help you a lot. personally im currently up in the air about getting the bilstein b12's or ohlins road and track coilovers.

I have H&R springs on my 997S & the ride is about the same as when it had stock springs

Every time I put just springs on a car I swore I'd never do it again. Well, I'll never do it again.

I never had any issues with both my 997 S (.1 and .2) suspensions and I prefer taut to soft. Both had PASM and I'm no fan of PASM. Sport mode was useless with both cars. Doesn't surprise me your strut blew. Seals can easily blow when more pressure is applied.

Harsh ride could be from a number of causes when just throwing lowering springs on otherwise stock dampers. Dampers in general are tuned for a specific spring rate range. You can put 10X spring rate over stock on a car but with well matched dampers are just as critical, correct valving dampers produce both incredible grip over any paved surface and exceptional ride quality.

Isn't the spring set the missing part of this conversation?

I have only lowered a 964 using springs only and I do not remember the ride changing that much. I used coil-overs on the 993 and there was a definite change in ride quality. I was expecting the change though so it did not bother me. I've done absolutely nothing to my 997, except drive it like I stole it, at least once each and every day!