Put it to use. Interarms was just the previous importer of Walther pistols.

While they're far from rare, they are often more desirable than the newer versions made by S&W. I doubt you'd gain much by selling that one and buying a more used one though.

It's likely that you could sell yours and buy a new one from S&W, but the consensus from the Walther owners I've talked to is that they'd prefer a used Interarms over a new S&W. Fit and finish are generally better, and few changes from the original German design. The S&W models have an extended tang, and a change in the hammer block that prompted a recall recently.

(My S&W made ppk/s is working just fine though.)

You didn't say what cal it is.
No matter, I suggest you go to the P38 forum. They have a section for post war PPK. Be prepared to post photos. I have an Interarms PP in .22LR. IIRC it cost me $200+. It is now worth about $800. I've relegated it a semi-safe queen. They ain't making them any more.

Walther Forums has a place dedicated to PP, PPK and PPK/s.
Mine is an Interarms I purchased in 1984. I shoot it once in a while at the range and carry it sometimes. It is a well made gun with a better finish than the S&W.
It was made to shoot., at least once in a while.