How to assert data type of a particular node value and desired no of decimal points ?

Here is the simple script to Test the data type. And result shows that all the element values are being treated as String only. So in your case you have to parse to the required data type as you know it from the schema. 

def xml='''
<xml>
   <node>
      <val1>1</val1>
      <val2>12.00</val2>
      <val3>true</val3>
      <val4>testvalue</val4>
   </node>
 </xml>'''
 def groovyUtils = new com.eviware.soapui.support.GroovyUtils(context)
 def reader = groovyUtils.getXmlHolder(xml )
 use (groovy.xml.dom.DOMCategory) {
    for( node in reader.getDomNodes( "//node" )) {
        node.children().each { child ->
            if (child.text() instanceof Integer) {
            	log.info  child.text() +" is integer"            	
            } else if (child.text() instanceof Double) {
            	log.info  child.text()+" is double"            	
            } else if (child.text() instanceof Boolean) {
            	log.info  child.text()+" is boolean"            	
            } else if (child.text() instanceof String) {
            	log.info  child.text()+" is string"            	
            }
        }
    }
}

 Output:

Fri Feb 13 07:46:03 IST 2015:INFO:1 is string
Fri Feb 13 07:46:03 IST 2015:INFO:12.00 is string
Fri Feb 13 07:46:03 IST 2015:INFO:true is string
Fri Feb 13 07:46:03 IST 2015:INFO:testvalue is string