No point in removing them, just make +1 the main bonus, then a small bonus as +2 and finally a little gain as +3.
+2 often gets like +1 speed which considering the other buffs from looming is worthless. +3 gets you +1 stab and +2 swing usually.
Why not something like +1swing, +1stab, +1 speed at green then +1 swing +1 stab at blue then +1 more swing at purple.
For armour +3 at green, +1 more for blue and purple
That is better diminishing returns and will open up the market so people don't just trade +3's and newbies can get some useful gear sooner