Does increasing the replication factor improve read latency?

It depends on your read consistency level. If you're reading at *_ONE, it won't make a difference. If you're reading at *_QUORUM, it will likely increase latency (more replicas to read and reconcile).

In short, increasing the RF will not improve (lower) read latency. In fact, the best case scenario is that it doesn't affect it at all.

On the other hand, if your cluster is serving tens of thousands of reads per second, adding nodes (with the same RF) should improve read latency. This of course is assuming that your current cluster nodes are overwhelmed during high throughput scenarios.