“Photography is a complex and fluid medium, and its many factors are not applied in simple sequence. Rather, the process may be likened to the art of the juggler in keeping many balls in the air at one time!”
Ansel Adams, from the introduction to The Negative - The New Ansel Adams Photography Series / Book 2
As for the APO vs. non-APO matter, I once looked up and compared their respective performance data (MTF, distortion, fall-off, chromatic aberration). If one thing I learned it would be that stopped down (f/5.6) and at moderate enlargement (10x) there is no discernible difference between the regular Rodagon 50mm f/2.8 and the Apo-N version. The non-APO is a superb lens.
Yes, they may not make any difference in the range that we do most often. We can't even tell if there is any difference. The difference may show when you try to stretch to large enlargement. But at least we know that both lenses mentioned are superb lenses, or the best in this category.
A photo amateur
Sinar P2/F2/Nikon F100/Bronica ETRSi/GS/Saunders 4550XLG/Jobo CPP2/CPE+/Colorline 7000