284 and 292 are the duration of the cams - basically how long the cam is open. The longer the duration basically the greater the amount of air the cams can let into the engine.
Longer duration cams will shift your power band to the right - so give you more power at the expense of torque down low. In essence you don't gain any area under the curve generally, but for racing type applications, obviously you want all of your torque at high RPMs to make more power.
Without a doubt changing the camshafts would require retuning to get the most out of them. Personally on a car with variable intake and exhaust camshaft timing, I wouldn't mess with the camshafts unless it was from a very reputable tuner (e.g. Dinan) who had done the extensive R&D and fine tuning (i.e. offering in a "package" with camshafts and appropriate tune) necessary for this type of modification on this type of engine.