Nikon Capture is definately worth having!
First off, you don't need Capture or Photoshop for RAW Conversions. The free Nikon View program (download from NikonUsa.com with your d70 serial number) will do RAW to JPG conversions just fine. It just can't make any adjustments.
I'd recommend passing on Photoshop CS, and get Capture for color adjustments and PS Elements for editing work.
Personally, I find Caputure a lot more intuitive and easy to use than PS CS. The Curves, White Balance, and D-Lighting features are easy to use and do an excellent job. Plus, if you want to upload Custom Curves to your D70, you are going to need Capture to do it. Custom Curves are a VERY effective tool to get better shots out of this camera without post processing.
You'll need a photo editor like Elements to manipulate content, but you can get pick that up for about $500 less than PS CS and get 90% of the functionality.
Dave