Trust me, if I saw a real difference between prints from Neopan 400 and Tri-X, I would have never switched to Tri-X a few years ago after shooting Neopan for 10 years.
Maybe not in prints, but if you do a modern scan of your negatives today, I am sure you will appreciate the difference.
Even if the grain-difference and resolution-difference "is not visible" in your prints (after all, you manually focus to print anyway, which is a source of error), the devil IS always, has always and will always be in the details.
I do a lot of digital post-processing and when I do things at 300% enlargement, that are normally not visible when you look at the whole picture, it still gets much better after doing it, it's almost weird how that works.
Neo did have the upper hand on Tri-X regarding grain and resolution, there is no denying that, the fact that you could not see any apparent difference in your prints, doesn't necessarily mean that there was no difference.
For the record, my own substitute for Neo is Tri-X and I like it and feel they are very similar, unless you start scanning them and check closely...