ReadyBoost is not designed for this type of usage. ReadyBoost is designed for low-memory machines, which your machine is not. Your computer simply has to much memory and cache to gain any improvements from ReadyBoost.
ReadyBoost provides the most significant performance improvement under the following circumstances:
- The computer has a slow hard disk drive. Computers with a primary hard disk Windows Experience Index (WEI) subscore lower than 4.0 will see the most significant improvements.
- The flash storage provides fast, random, non-sequential reads. Sequential read speed is less important.
- The flash storage is connected by a fast bus. Typically, USB memory card readers are not sufficiently fast. However, connecting flash memory to an internal memory card reader might provide sufficient performance.
See this article.