I've used K&N on my car-type vehicles, lately put on a new, similar product from afe, another performance filter that claims to have deeper pleats for more surface area.
The orginal owner of my moho brought it to Banks (www.banskpower.com
) and had the intake and exhaust upgraded, so it sounds great and is reputed to have more power & better mileage (usually about 9-11 with toad and a heavy foot). Banks may offer an upgraded intake for your model, check their website.
An engine is "just" an air pump, and uses the right amount of fuel to keep it going. Most OEM designs constrict both input & output so a well-designed aftermarket sysem can help performance, and hopefully keep the water out.