If ANY of them are likely to become collectable, and that's questionnable, I'd say it would be one of the Genuine, original, Eibach Cougars. There weren't many brought here, but they featured a three piece bodykit, Eibach suspension, Eibach 17's, bonnet scoop and a rear wing.
Unfortunately I don't see any of the standard Probes or Cougars becoming collectable except maybe to those who appreciate something unique and different.
I can only speak from driving my own car that the Cougar is a great car to drive and handles well. The V6 is great and reliable.
That's my 2c on the topic anyway
Dan