Is the amp beginning to hum, make any other noises, or otherwise sound like it is going bad? Does your amp run hot all of the time? If it is not acting up, and it is not an amp that subjects its internal parts to high heat levels, I would not worry that much about the state of the capacitors. You could have someone just take a look under the cover for bulging/leaking caps, resistors that look a little burnt, etc. If your tech looking under the hood can do in-circuit tests of capacitors (equivalent series resistance (ESR)), he might be able to spot one going bad without big hassles and high labor cost.
A preventative replacement of all caps seems extreme to me.