It's not working because you are converting to a string and trying to traverse an object property tree
You could do it like this, $VM."ExtensionData"."Guest"."ToolsRunningStatus" but I don't see how that would help.
Why not like this, (plus wicker faster)
$VMViews = Get-View -ViewType VirtualMachine -Server $vCenter -Property Name, Runtime, Guest | Sort Name
$VMViews | Select Name, @{n='PowerState';e={$_.Runtime.PowerState}}, @{n='ToolsRunningStatus';e={$_.Guest.ToolsRunningStatus}}