It was the budget model in the "K" series of camera, while the Spotmatic was (in the mid 60s) the top model from Asahi Pentax. Also, at some point in time the production of the K1000 was shifted to japan to China with a bit of reduction in build quality.
Sorry to burst the myth, the K1000 is perhaps the most overrated 35mm manual focus camera. It is a perfectly fine camera, but it is ridiculous that even today a K1000 on the secondhand market is more expensive than a -for example- K2 and KX, directly comparable and superior. Or sometimes more expensive than a Canon FTb, a superior camera in all respects.
-- end of my rant --
I love the spotmatics, by the way.