A lot of good advice here. I bought my first plane 31 years ago, with no real plan for it succession, and I still have it. I support the idea that in this era of older planes, approach your purchase as you might be the last owner of that plane. Buy well within your means, maintain it so you can fly it, and fly the heck out of it. Don't expect to recover investment you have made in it, other than lots of great flying. If you can sell it later, bonus (though you may have to give it away), but maybe you just own it into it's retirement.
Have the aircraft really well inspected before you commit. For a Cherokee, confirm that the wing spars and primary structure are okay. I am aware that for some older Pipers, Piper will not provide parts. I have this first hand from Piper. Much of the structure of the aircraft can be repaired by simple sheet metal work, not requiring Piper parts, but a few primary structure parts, like spars, cannot be made in the field. If you can't buy them, you're grounded. Corrosion on the wing spars could be a concern, particularly if the aircraft lived near a salty environment.
The aircraft manufacturers did not intend that we operate these older aircraft anywhere near as long as we have. For some, more intrusive inspections are being mandated, and that's not a bad idea. For many, the manufacturer simply has no interest in maintaining a parts supply for the older aircraft, when they could sell you a brand new one. Do your homework, and inspect the plane!