Most of us can't seem to fault our bikes, especially when they are new and shiny. Riders are stunned at how much better their new bike can feel after a suspension set-up, despite thinking it was already the best bike they've ridden!
For trail bikes and up, tires, dropper post, and contact points are high on the list for sure. Bike fit for XC riding/racing and road, absolutely.
In the #5 category, I'd add new shock pump. These have about a year of life in them with normal use. Start fresh with a new bike to ensure you are consistently running the desired pressure in your fork and shock.
Make sure to not over-tighten the head of your new pump onto the valve of the fork or shock. You will end up wearing down the pump and compromising the accuracy of your reading. Only tighten the head of the pump until you see a steady reading on the gauge, not any more (needle rises to pressure reading, then stops). This will ensure that the only air you loose when removing the pump from the shock is from the hose, not the shock itself. Always listen for a brisk, short release of air. Your pump will have a much longer lifespan like this as well.