Peter
It is really heartening to know about your forthcoming Indian trip. And the route which you have chosen i.e. Delhi to Goa is one of the best in the sense that upto Mumbai outsirts, you will witness long high speed runs & added advantage of beautiful scenery between Mumbai & Goa as the train will pass through one of the most challenging engineering marvels in the world i.e. the Konkan Railways. I've always wondered why don't Nat Geo or Discovery show a documentary of this route???
Now coming to the Rajdhani, I...
more... feel what sets it apart from others is its speed & comfort levels. It's allowed to run at the maximum speed possible i.e. 130 kmph and till very recently it used to be the only train touching that mark along with the Shatabdi express which is a fast intercity express.
Its distinct livery sets it apart from others plus I was a frequent traveller long time back in the Delhi-Mumbai Rajdhani. I have always loved high speed trains & it's right up there with the best. Plus add to the fact that you are planning for 1 AC, I think there's no better way of exploring India than in the highest class on offer by a very prestigious train i.e. Rajdhani 1st AC. It's a different fact that its livery has been enroached upon heavily in the present day such that it might sometimes become difficult to spot it at 1 go. But nevertheless, the aura of certain things just doesn't diminish with time.
Regards...Ankur