I have two 28/3.5 AI Nikkors. They are both very sharp. The 28/3.8 AIS is supposed to be better in the close-up range. If I need to be in the close-up range and I do not need the 28mm focal length I just use a 55/2.8 AIS. All of the 28/2 Nikkors are supposed to be very good so yours may not have been in good condition.
you picked a good real-world representation for your sample image test.th3.5 seems obviously better. Ithink, what you see is whar you'll get.