The WAN acceleration technology aims to accelerate the broad range of applications and protocol over the wide area network. The acceleration techniques include low level compression, intelligent bit wise compression and specific protocol optimization. Adding more bandwidth most of the times will not improve the end performance of an application over the WAN.
The performance profile of many applications is defined by the latency of the connection. Adding more bandwidth will help with the concurrency of the connection but will not improve latency. This is because most protocols have an element of serialization, which means that they require a response to a packet of data before they can send the next one. Clearly with more bandwidth more conversations can happen at the same time but more bandwidth cannot speed up the time it takes to send and receive a packet of data.
WAN acceleration does address the latency issue by being very selective about the data that is sent over the WAN at both a protocol and application layer.
Therefore, it can be concluded that, WAN acceleration reduces the effects of latency, but by increasing the bandwidth we cannot solve WAN performance issues.