Is brute forcing a private key with unspent coins getting easier? Is the likelihood of correctly guessing a private key with unspent coins increasing due to:

More addresses being used resulting in more private keys with unspent coins (i.e. higher chance that a random private key might have coins).
The fact lots of people use deterministic wallets (i.e. one could discount billions of deterministically generated private keys if the first 20 are empty).

Is this significant in terms of security?
It's increasing from approximately zero to approximately zero.
Since the starting seed of HD wallets is essentially random, I don't think this helps.
This isn't significant.