We all have our own personal set of references on the subject. Mine have evolved a bit over the past 10 years.
The simple answer is it depends on "what do you like" and it relates to "how do you smoke?" If you are a mouth only smoker with no nasal exhale aging NC's, which are typically stronger will definitely change them, but you might not appreciate/notice or like the change. Getting milder, more rounded might be experienced as "going flat" if you are not doing the nasal exhale.
For me, aging of some NC's (typically high end for me) has mellowed them to the point where I can do more nasal exhale and I enjoy them more. But, typically still have the same problem, it takes conscious effort to modulate the nasal % of smoke and makes it hard to relax when smoking one. Invariably I get distracted and do too much and get zapped.
I think there are some awesome NC cigars that over time become "the poo" Padron anniversario's, OPus X come to mind. And like Cubans you will find random stuff that just gets great for reasons unknown to us.
The economics are interesting though. I tend to compare high end NC's to pedestrian Cubans both fresh and aged. Smoked a 15 year old party short and a 15 year old Opus x the other day... both were good but would choose the party short 10x out of 10 and it was $ 4 vs $15 at time of purchase. Part of my preference was that the Opus still was "potent" and required thought and conscious control of the nasal % at all times, vs the short that I could nose to my hearts content.
Maybe our frame of reference is just not complete enough. Another 10-20 years and we might all be kicking ourselves for not collecting and aging NC's for their then realized 40 years to get good/mellow enough for us nasal exhalers to love.