I honestly think a manual detonation would make it overpowered. I love the Mine launcher and those I fight against know how devastating it can be when used right. The times I miss my shots are when I don't cater to our ship's movement, or they're just out of range. With a remote detonation, I'd probably be hitting 70% more of my shots, and it only takes two mines to really ruin someone's day.
The fact that they only explode when hit by a ship or another mine gives it a requirement of experience, timing and trigonometry. It's difficult to use, and therfore, balanced, not to mention fun.