Would one saddle be appropriate for a foldy and my Nomad or would it wear in different places???
Richie,
So long as your position on each (different) bike is the same, the saddle should be freely transferable. The sit-bone impressions made on one would work on the other. All my bikes are set up so I can duplicate my preferred position, and I've had no trouble transferring saddles from one to another.
However (you saw this coming, I know), if your position differs greatly from bike to bike, then yes -- the saddles will form to a specific bike.
The key here seems to be whatever affects back angle. As the pelvis rotates forward (result of a forward lean), the ischial tuberosities (sit bones) become effectively narrower. As the pelvis rotates rearward, it becomes effectively wider (as when sitting uprght). That's how saddle wear patterns are most affected.
Either of the bikes you mentioned can be made to pretty much duplicate your position on a larger-wheeled bicycle. The key question is, do you want to have the same position? If you do, then no problem switching saddles between them. If you don't (and many people seem to prefer a more upright position on small-wheeled Folders), then you'd likely want different saddles for each bike.
Where Bike Fridays are made here in my town, I was going to mention some things to keep in mind when selecting a small-wheel folder, but that is beyond the scope of this Forum, which is geared primarily toward Thorn Bicycles. Richie, you're welcome to contact me off-list if you wish to discuss the particulars of Folded touring in greater depth.
Best,
Dan.