Dreams are shorthand, and use symbols to represent things you are thinking about in the present. In other words, your ex in a dream is not your real ex, she is instead standing in for something in your life that you're thinking of lately, possibly something that was satisfactory for a long time and then had a brief bad ending, after which your life went on well without it. (Only you can tell what your ex stands in for, as a symbol.) But as you say, the dreams seem to be about the good parts instead of the painful part. Maybe you're going through a time where you are no longer feeling the pain of bad things that have happened but are long done. I don't think it means you are supposed to see her, or develop a further relationship with her, I think she is merely a symbol for something more current. One way to assess this is to think of how you felt in the dream, and then after you identify your feelings associated with the dream, ask yourself, "In the last couple of days, when have I felt this same way?" It might not be anything related to your ex wife, but follow the emotion. You might be able to identify what she is standing in for.
Yes, perhaps the above is playing a role. Or it is random. You can do some soul searching but please don't take this to mean that you made a mistake 25 years ago. good luck