As a go-forward strategy when refreshing the Aruba Cloud is definately a consideration, as are newer Aruba controllers (the 7xxx line of controllers).
Key to the Aruba cloud command&control are Aruba Instant access points (IAPs). To leverage the Aruba cloud option you would place IAPs (or RAPs that are IAP capable (RAP3, RAP155, RAP109 and so on) at your sites and use the Cloud as the centralized control, management, monitoring point.
What kind of access points population do you have today ? (model(s))
As for our friend the 3400, it does have many years of service infront of it planned yet. FYI, Aruba supports all devices for 5 years post End-of-Sale (EOS). The 3400 has not been EOS'ed as of yet. aka. you can think of it as having 5+ years of run time on that platform yet.
JF