Why would I buy these versions i already own PC versions?

So does that mean there is really nothing new or different in these versions ... aside from perhaps some difference in the look and feel, which is likely less than the existing PC versions?

There are differences, but they're really minor. E.g. while in the Irish pub in Broken Sword 1, there's no violinist inside et cetera. Games used to differ a bit between platforms back in the days, but in this case it's nothing major. And with the PSX versions, the graphics are obviously inferior to the PC ones.
Essentially these are the same games, just presented in a slightly different way than on the PC.