You could get a second 3060 Ti and it would speed things up in a number of ways, depending on how you want to configure and make use of it (both cards on a single image, two instances of Blender with one rendering using a single card while working ‘normally’ using the other card).
However, a couple of things to consider. A 3060 Ti isn’t exactly super fast to start with, for example, 2 of them are around the same as my single 3080 Ti, while a 4070 Ti is actually faster while using less power. Then of course a 4090 just blows it all out of the water, being over twice as fast as my 3080 Ti.
Then there’s the second issue, the 3060 Ti is only a 8GB card and having two or more, still limits you to 8GB, so if your renders as getting more and more complex, you are going to hit that wall.
Even 12GB in say a 4070 Ti isn’t ideal, but it is at least better, with once again, the 4090 and 24GB being the real solution.
Either way, don’t do anything just now, since in a couple weeks, Nvidia will expected to announce a ‘super’ series refresh and there’s a fair chance there could be something like a 4070 Ti Super with 16GB for around the same price as the 4070 Ti currently.