Ok...if wer're going to get technical here...
Vader's body wouldn't have smelled any worse than hot metal and burning fabric...after all, according to Obi Wan, he's "more machine than man, wretched and evil."
So, what Luke actually would have smelled was the uniform of Vader burning, along with metal...the smell of burning flesh would have been in there, but not as strong.
But, that's only if we're getting technical....
Nice one, just at lunch time here rofl!! Ok then why did Obi Wan's body disappear when he was killed and not Darth Vaders?