Technicaly, statistics is just theoretical value to model the most likely outcome. It does not mean that is the true model of what will happen.
Imagine this, if you have a statistical chance of surviving tomorrow of 99%, does that mean you will survive tomorrow? the answer is, that you are very likely to survive tomorrow.
but you still have that 1% chance of getting hit by a bus, train, killed by a mad scientists, escaped penguins from the nearby aquarium, or maybe even stepped on by a 100 metres tall mechaloid (piloted by some idiot, say..... shinji). 
So likewise to upgrading stuff, if your luck is hiding like wally does, then by all means upgrade it. However if your luck is like trying to get a penpen to quote shakespeare then you are better off borrowing somebody else's luck.
