Question on old postcard collecting

[darkhorse9]

I know there are several people on here that collect vintage baseball related postcards. Some of them are really cool and would be a good addition to my collection.

My question is, though. Does having them written on and a postmark raise or lower the value? To me it would seem to raise the value since the date of issue is guaranteed. That's counterintuative to collecting anything else, though.

I'm sure it's been asked and answered before but I came across some neat old postcards that I might have wanted, but they were in excellent shape with no writing or postmark, so I passed on them. Hopefully I didn't miss a deal.