I think dante is a counter to anything but 6+ spectres (4500 worth, plus the energy to fund them).
But Dante is a big clumsy dumb unit that loses games with its tardiness. I would prefer to not have to switch to strider to deal with a 750 unit.
I've not yet tried it, but I'm thinking that eraser will allow you to negate all spectre targetting, and then you should be able to just walk all your cloaked warriors or whatever into their rock/warrior blob and kill it. Follow up with glaives to secure kills on spectre.
Alternatively, thunderbird + glaive ball should work.
The more general answer is to apply more pressure somewhere else, to bait shots with patrolled scouts or nanoframes, or to target their energy production.