Iight, now heres a couple of things that I like in different Dbz games that I had played in the past.
One. This one is for saiyans(Class.Low Class:means you are very very in the beginning but will become stronger over time and will most likely have good stats. Normal:Means you will be a average fighter and won't have really anything abnormal. Elites:Very strong in the beginning but must train hard to keep your advantage. Legendary:Its a chance you may be this your will be OP to most newbies.
Missions:Just like in GOA except you can do it again once you already finished on.Get money slowly but when u use your "zenni" you will be able to buy something that will help you out like a battle armour that can absorb some hits.
Planet Destruction(found that on another byond Dbz game) Must use a powerful tech to do that and at which countdown starts till' it exploses and everyone dies.
Fighting Styles(Found out On Lost Saiyans) Have a varity of Teachers to show you different styles. Make it so you must master the style.
Don't make it so every person you see has Ssj on make it abit of a challegne.
War system:Red vs. Blue: You can't hurt your own team mates have to elimate or get up to a certain amount of kills.
Fractions:Rogues,Loyalists,Traitors...etc.Make it so that once a certain fraction reaches its "point" that they get to Destroy a Race Like what Frieza did to the Saiyans.
Make it so When you make a character you are born on that race's planet.(goes god with the Blowing up planets idea.)
Make a mission example: Ryu,Prime,Zero,Eternal,and Ten must go to Earth and wipe out the inhabitiants.
An idea to go with this is Npc's races like have guards like in GOA walking around to help fight of invaders.
From M.I.K. (Ten is my name ingame)