I'm not sure why you add 'c' instead of subtracting it? Connections are an advantage, so if you want to balance things out, having many of them should lower the bonus value.
Connections are an advantage when expanding
, but they are a disadvantage when defending
: a bonus with lots of connections is much more vulnerable.
So there is something to say for both: they can be worth less because they are easier to take, but they can also be worth more because they're harder to keep.
I feel it depends on the rest of the map. If it's a big map where most bonuses won't be on the front lines, more connections should lower bonus value. If it's a small map where most bonuses are under direct threat, more connections should increase bonus value.