Embarrassment with .NET URI

I need to work with the URI in .NET. What I need to do is:

• Parse URI from a poor string to be able to extracts its parts
  
  • name/value pairs of a query;
  • scheme
  • host
  • path
• Generate URI based on
  
  • name/value pairs of a query;
  • scheme
  • host
  • scheme + host parts
  • path
• Modify URI the same way
  
  • name/value pairs of a query;
  • scheme
  • host
  • scheme + host parts
  • path

There are basically 2 types in .NET that can help with it: Uri and UriBuilder. Neither of them allows me to do all the things I mentioned properly.
Uri class does not give name/value pairs. So I have set of extensions to do that. Not a big deal, but it is not there, in .NET.
UriBuilder has a ridiculous bug; and guess what. The status is Closed as by Design. WTF! Just insane!
What a shame on .NET. How long should I concatenate the strings and use my own utils when things are a bit more complicated that just absolutely simple? Sick and tired of that.
I definitely need to get my hands on some RFC and implement it properly.