As which race are you playing?
Because the TechDefs.xml file is used for races that do not have a specific tech tree.
For the Terrans you should change the TerranTechDefs.xml, for the Thalan you should change the ThalanTechDefs.xml, etc, etc...
This means that if you want to change the research cost for all races you will have to supply modified versions of all the *TechDefs.xml files.
Note: You did not alter the research rate you altered the research costs.
If you want to alter the research rate you should look in the PacingDefs.xml file.