Aha, indeed, it works now.:smileyblush:
There is one downside. The execution time now takes 10 times longer. 
$row.VMs=[int]$($_.vm.count)
$row.VMsHosted= [string]::Join("|",(Get-View $_.VM| %{$_.Name}))
$row.Hosts=[int]$($_.host.count)
$row.HostsConnected= [string]::Join("|",(Get-View ($_.Host | Select -ExpandProperty Key) | %{$_.Name.Split('.')[0]}))
It seems that these (red) lines retrieve all properties of VM resp. VMHost and than pass only the names back which slows down the total execution time of script.
thanks in advance!