Ultimately, what you're trying to do with the EXTRA blank lines between each one is a little confusing :)
I think what you really want to do is use Get-ItemProperty. You'll get errors when values are missing, but you can suppress them with -ErrorAction 0
or just leave them as reminders. Because the Registry provider returns extra properties, you'll want to stick in a Select-Object that uses the same properties as the Get-Properties.
Then if you want each property on a line with a blank line between, use Format-List (otherwise, use Format-Table to get one per line).
gci -path hklm:\software\microsoft\windows\currentversion\uninstall |
gp -Name DisplayName, InstallDate |
select DisplayName, InstallDate |
fl | out-file addrem.txt