A lot of it has to do with how these effects are applied and it what order.
A gradient as the second effect on a shape will completely cover up the first effect... unless one of the colors in the gradient is set to be transparent.
If you put the gradient first then other effects will show up over it UNLESS these effects ALSO have colors set that would hide the gradient.
Let's say the base fill color is white. If you add a gradient that is white to black the white in the gradient is "redundant" and also will hide other effects if it is the first. You can make the first color of the gradient (white) completely transparent and now the base color shows through and the gradient fades to black and other effects show through it as well.
You can also have more than 2 effects by using styles. Imagine... by applying two styles AND using the effects in the base shape you can have up to 6 effects on one shape and up to 3 stroke effects (be careful... this may open a rift in the time space continuum).
This one shape has six fill shape effects and 3 stroke effects. 2 fills effects for the base, 2 fill effects for each of the 2 applied styles. One stroke effect for the base and 1 stroke effect for each of the 2 applied styles.
http://www.lowrestv.com/moho_stuff/6effects.moho
Most of my knowledge of effects came from just trying them out on simple shapes and changing the settings and order of use and doing quick renders.
Sometimes I get bored... and I just "play" with all the combinations of effects and styles to see what kind of funky results I can get.
To be honest when I try to do some funky effects tricks I usually am starting from "zero" knowledge. I keep experimenting till I get what I want or get close to what I want.
EDIT:
When applying a style to a fill shape that you only want the EFFECT to be seen do not check the Fill Color, Line Color or Line width check boxes for that style. If you do those attributes will overide the base fill and line styles of the shape. You may WANT to check those to change them based on the style. This may change how they render in relation to OTHER styles applied. The second style applied will override the first style.
Style two, if the line width is checked will change the line style no matter what style one is set for.
-vern