Yes and no. If you have Airwave, managing instant on a larger scale like you currently have is possible. If you only have a controller-based network, you should only deploy campus APs to centralize management.
With regards to redundancy, if you have support on your controllers, Aruba provides next-day hardware replacement, so that might eliminate or not make your need for another controller necessary. What I ask some users considering whether or not to add a controller for redundancy is to calculate your loss of not having wireless until the controller arrives the next day. If your business depends on wireless and your loss is much more than a controller, get the controller for redundancy. If not, get hardware support and it will be there the next day. Just my own opinion, however....