thats strange, i am the opposite, my stuff seems to work better plussing them when they are already blue
but yea, i have had some good luck lately too,
gave a hat 200hp, 4 int and plus2 it
gave all my gear some sort of blues that were not there before
and made my lvl 48 spear +5 with only about 4 elixers (from +3)
maybe alchemy success rates have changed?