Hi, The stylus certainly can make an improvement, but this is when you more from Elliptical to Shibata (very difficult to set up correctly) or even better & a little easier to set up Micro Line.
This is what several cartridge manufacturers do with the cartridge line Ortofon go from Conical with the OM5 the OM40 having a high end nude FG 70 tip. Similar with the basic Red cat to the Black. Again Denon did this with their DL-300 MC cart through to the 305. However as well you really need to also upgrade the cantilever at the same time. So you have the basic Carbon Fiber, then aluminum, Boron & even Sapphire.
But the statement that the cart is responsible for 95% of the sound is totally wrong. The arm is the biggest contributor, it is the arms ability to allow the cart to retrieve the subtle information from the LP grooves. I would put is about at a 60/40 split. A cheap cart on a good arm will always sound better than a expensive cart on a cheap arm.
Cheers