Is it worth installing .NET 3.5 to run the ISE? I use Powershell but only have .NET 4 which runs it just fine. I'm a little surprised that ISE requires 3.5.
It doesn't make any difference. It required 3.5 as win7 shipped with that framework. You may actually have 3.5 installed already. Check for the following dir: c:\windows\Microsoft.net\framework\v3.5
If it's there you have it already.