There are 6.5" component speakers, and I honestly could not tell you the difference. That's my lack of knowledge. But you should be fine if you are happy with what you have now. The system can drive 4 speakers now.
That being said, once you start spending some money, and figure out what an amp can do, then it's a downward spiral of cash! Someone can explain this better than I can. But what we experienced going from stock, to a nicer head unit and better speakers was cleaner sound, better tuner and more power.
When we added an amp and more speakers, the more power was cleaner, and the head unit didn't have to try to drive them all. Volume was better and sound quality at higher volume. When we added a sub, then we realized the lows were not being driven through the small 6.5" speakers and the whole system sounded better.
Of course a pair of amps, and a another pair of speakers and sub required a second battery, and isolator to protect our cranking a battery etc, etc. But you use these things, and it's money well spent.
My buddy just pulled his pontoon out of the stereo shop and had done similar to what we did. His Premiere pontoon had a nice Sony head unit and 4 kicker 6.5" speakers. Nice sound at low levels, but there was quite a bit of noise around the speakers, and they could not handle volume. They would crack at any increase in volume.
He had them put Dynomat around the speakers to kill the rattles and vibration. They put in a mono amp and a pair of subs. The head unit still drives the 4 kickers. with no amp. The sound difference is amazing just pulling the lows out of them. Subs are not really directional, but he had two installed as he is running a 23' boat.
It's all in what your checkbook can afford. But all of these items are building blocks.
Good luck!
