I run a stock 454 Magnum MPI in my Baja 232.

Will there be any noticable impact on the performance
of the engine if I install a K&N Air Filter?

It's really a flame arrestor, doesn't do much filtering. As an experiment I pulled off my flame arrestor on my 496HO to see if there was any sort of gain, the result was nothing. Don't waste your money IMHO.

Speed gains are expensive and usually start with exhaust, cam, headwork, and computer reprogramming. You can screw around with some prop work, but in my experience with a low power boat (28'/496HO) it too was a waste of time and money. I just dealt with what I had and eventually bought a different boat LOL!!

No worth while improvement. If you want to go faster, you'll find it in a prop, exhaust or a blower.

I put them on my 454 mags with no difference. But they sure look good.

No, Save your money

Ditto. Done the same thing with no results. Seen no difference when I owned a 502 mag a few years ago. If it did it would be so insignificant you wouldn't notice anyway. Don't get caught up in "trinket" enhancements. It's a waste of money.

That alone will not make a difference. Try the Arizona Speed and Marine upgrade kit, which includes the good looking K&N. That with exhaust will probably be worth 3-4 MPH Oh, it will be over 2K.