The table, which can be found here, includes, I think, every Disneyland attraction - not including shows and fireworks. Some attractions which are different in name only (Big Thunder Ranch Petting Zoo and Little Patch of Heaven Petting Zoo) have been consolidated as one. Active I've defined incredibly broadly as any attraction that involves input from the guest - so yes Buzz Lightyear is active, but so is Dumbo (you pull a lever) and Autopia and so on.
So what does the data tell us?
In Disneyland's history, 69% of attractions have been original and not based on an established media property.
During opening year 1955, 68.6% of attractions were original.
Of all the attractions that came and went during Walt's life, 76.7% were original.
At present, 46.2% of Disneyland's current attractions are original.
In Disneyland's history, 24.8% of attractions have been active.
At opening, 14.3% of attractions were active.
Of all attractions existing until Walt's death, 18.4% were active.
At present, 38.5% of Disneyland's attractions are active.
So there we go - some data to back-up (or refute!) people's claims. We can see here 'What Walt Did' as well as trends across time. I'm not intending to make any statement here (I'm not meaning to agree or disagree with any 'sourced attractions are bad' or 'interactivity is bad' points of view, or vice versa), I just wanted to contribute something to the debate!