Hey @jmit
Here is another trick to combine two modes. Using the default faded mode you can make a new column that will return a value based upon the row state:

If you then put this into the Size property of graph builder then selected rows will not only use the faded highlighting mode but will also size

By changing the value of the selected date you can change the difference in the size of the selected vs un selected markers. If you want the base level of the markers to be smaller, right click on the legend and go to size settings and make the maximum a larger value.
Also, you can change the default marker mode by right clicking a graph, going to "Graph" and change the selection there (vs going to the preference). However, you can only change modes, not tweak their settings.
Hope this helps!
Steve