Swap out one of those first two rewards with "Increased minesong duration." Maybe just another minute or two. A few points in abilities isn't interesting or all that useful, and as far as I've seen the "localized caveins" mean they're just further concentrated above your head, no benefit there.
It would be fun to come up with a more complicated minesong system though with benefits spreading to those nearby also engaged in a minesong, but it's all too easy to abuse.
