It will only improve the connections between your three wired devices. Not your connection to the internet for those devices. You could stream video to your TV faster, or transfer files between the computers faster. Of course, if it is already fast enough that you don't notice any lag or problems, then it's a bit like building a four lane main street through the middle of a rural town. Just a lot of unused road.
To continue the analogy, your DSL router is like a two lane hi-way to the next city. No matter how wide you make Main street, the traffic is only going to come and go as fast at the road out of town.