The ppk was the original DA autopistol manufactured by Walther. The ppk/s was manufactured for the US market after the gun control act of 1968 made importation of the ppk illegal (too small). The ppk/s is generally just a Walther PP frame with a ppk slide. I don't think any ppk/s would qualify for any "collector" status.
They are fine for shooting though With the short barrel and snappy recoil, you may find that a larger handgun would be better for your first though.