The effects of devestation simply go to settlement mechanics.xml and find this.....
</factor>
<factor name="SIF_DEVASTATION">
<pip_modifier value="1.5"/>
</factor>

lower the 1.5 now when there is dev in our province you wont loose so much money.

unit speeds is in battlement movement (in the data folder) you can change the speeds on the different ground types. simply increase the entries per type and there u go.

Now to get rid of the dev on the world map (as in graphicaly) its either in the data/world/base folder or its in a xml file. I havnt found it to get rid of it and i have been working on lower the seige attrition rates but cant find em in the files. So for now, lower the sif entry so there isnt any effect except visual.