I agree with everyone....looking at all the above posts....

1. Tighting up the system will just move the natural frequency of the system (airplane) up to a higher speed...if that speed is higher than the plane can obtain you are good. This is true in full scale airplanes also.
2. Damping the system will increase the natural frequency of the system (airframe)....sealing the gaps, tight control surfaces, rigid control surfaces (use hard balsa), tape on the outer part of the aileron connecting it to the outer wing tip, a silicoln bead (use clear) in the aileron gap then when dry slit it, thick torque rods...I could go on will stiffen the system and raise the natural frequency...and raise the flutter speed.
3. Balancing will make the system will make a self damping system.

Most model airplanes that are not large use 2. to dampen the system. Most full scale airplanes use 3. One full scale LSA uses 2 and have had problems with flutter...the recomendations were to check the rigging on the ailerons to make sure they were in spec on tensions (slop).

Steve