I would agree with most of the posts. A few grams on a seat post is less than the difference between a full and empty water bottle.
I wouldn't worry about different wheels being an issue, but if there is one place where you might feel a difference is by getting lighter wheels and tires. You would appear to have 36 spoke wheels. A 32 spoke wheel with lighter rims, lighter tires will feel lighter and accelerate faster. The actual gains may not be huge, but it will feel faster. Revolving weight on a bike means more than static weight. Many cyclists have two sets of wheels.