Having a PDK I can't really comment on this, the 911T I test-drove had a hard but not impossible clutch, it was just that the range it engaged was a bit short (finicky) which wouldn't be a good thing for my better half. The only other car that felt like this was a 370Z I drove years ago.
Anyway, I think a trip to a mechanic is highly advisable, I don't know if at the end of the clutch life the spring feels harder, my son three weeks ago had to replace clutch and flywheel in his Mazda and (according to him) the only signs were very small range of engagement and a stiffer clutch, no slipping. No trace of friction material left either. Just a scorched flywheel.
Perhaps the previous owner consumed the friction material doing launches, to show how fast he was...