Ground planes are not only for high speed, the EMI performance of going 4-layers is easily one of the cheapest gains to be made in modern electronics. The other gain in this scenario is that you could tighten up the rebound times, which reduces input latency.
Can you pull it of with two layers? Yes, of course, but if you are charging $1000 for the thing I expect you to go 4 layers.
Can you pull it of with two layers? Yes, of course, but if you are charging $1000 for the thing I expect you to go 4 layers.