The K&N filter will give you maybe 2-4 hp, if that. It all adds up though. Say you did get a performance chip. What the performance chip will do is keep the intake valves open a little longer to deliver more fuel. When you increase the fuel you need more air as well. That 2-4 hp will increase to 5-7 hp if and when you do add a performance chip. It is an exponential increase, not a linear one.
You would be better served to get a cold air intake (CAI) instead of the K&N filter. The CAI puts the air filter further away from the engine to get colder air coming into the engine. Colder air = denser air which the engine's computer senses and adds more fuel which translates to more power. A CAI costs about $200 and gives you about 6-8 hp.
As far as the bigger exhaust goes, that will give you around 8-10 hp if you get a CAT-back system. The CAT-back exhaust is a larger diameter pipe from the catalytic converter back to the tail pipe, including a muffler. These normally cost around $500. There are systems that are not so loud.
If you were to add the CAI and Cat-back exhaust, you can add from 12-15 hp. If and when you add a performance device to your engine's computer, it will take advantage of those modifications even more.
The reason Honda does not put a high flow air filter, Cold Air Intake, or bigger exhaust is because they want their vehicles to appeal to a wide range of people. Grandma doesn't want a car that is sporty.