I have the same boat (1997) with a Honda 90. You should not be experiencing that "water spout" in front of the motor. Several thoughts.
First, the one you raise. When you said you removed the "cavitation plate" I assume you meant an add-on such as a Doelfin or similar, right? (Since you can't remove the REAL cav plate, which is part of the motor's lower unit. On mine, my motor's cav plate is almost exactly even with the lowest point on the keels of the sponsons, the bottom of the v's in other words. (Where you can see the drain plugs on the stern of mine.) When planing it runs just slightly below water level. (The cav plate, by the way, is the largest of the three flanges on the lower unit, and is the bottom one. It's clearly visible in the pic of my motor.) My motor is mounted in the second hole from the top, and I would think that if yours is as you say, it is too low.
Second, I have linked a picture below. Note just below the motor and below the transom, on the "bulge" in the tunnel which is to smooth conditions in the tunnel for single engine cats, there is a ninety degree stainless plate. It is a little hard to make out in the pic (the arm of the lift sort of blends in with it,) but you can clearly see the four bolts which mount it. AFAIK, that was a factory item, but anyway, its exact function is to kill splash which might come from below as you are describing. Does your boat have such a piece? By 2001, a different maker was building the Seagulls and may have left that piece off. It is easy to add.
Third, you don't state your RPM's at wide open throttle, but the spec on the 90 is 5000-6000, and I believe the 130 is the same, or very close. My 90, with full gas and just me in the boat, will deliver a top speed of around 35 (MPH, not knots) at about 5650 RPM's. Yours is way off. Besides engine height, prop type is an issue. This boat does poorly, generally, with a three blade prop. Do you know what you are running?
I guess I'd first try to get the motor at the right height, and I'm sure that will up your top speed. If that doesn't stop the "spout" then if you don't have the little SS bracket I'm referring to I'd consider adding one. Last would be the prop.
Well, enough for now. Let me know.