To be honest, I feel like the upgrades are extremely underwhelming. If I get a new piece of gear, I gain 2 or 3 defense when I have over 700 defense. The only real gains I see are in VIT which will boost my HP by at around 100 or more per gear upgrade. I certainly don't feel like I'm defending any better with tiny defense increases; I just get more HP to take the same amount of damage.