A motor built in 2009 that didn't come from the factory with platinum or iridium plugs is odd. A smaller gap, and it's a small gap by today's standards is also odd, changing it now is REALLY odd...and yes the firing tip is changed as well.
I think if a person stood back and looked at all these oddities they would arrive at a conclusion: that being something like combustion chamber temp is too high not saying that's it, just saying all the oddities if you look at them one by one......all those changes produce the same result independently.
If the boots and springs were the problem, why the dramatic plug changes and as I said the new and old boots and springs look identical, same markings on the new boots as the old boots, maybe diff material but I say not.