Does upgrading from 16GB to 32GB of RAM speed up video exports?

Yes, but only if your export is actually running out of memory. Video export speed is mostly about your CPU and GPU — RAM matters when you run out and your system starts swapping to disk. If you routinely see memory usage spike to 14–15GB during exports, 32GB will prevent that slowdown. But for a simple 1080p timeline with no memory pressure, 32GB won’t help at all — check your system monitor for swap usage before buying.