In reality you usually end up only using 2, maybe 3 special attacks per fight, unless you are fighting a group, an elite or another player.
Saving enough rage in a group for a few thunderclaps is usually a good strategy, and for elites you will need Mabinogi money that hamstring more often than you might think.
However, it is when fighting a player, especially a caster, which you will need to manage your rage most closely. Always save enough for the shield bash you need to keep your opponent from getting that last second heal, or final devastating spell.
If you are out of rage in these situations, you may just be running back to your body very soon.
You've probably noticed if you've already started playing that you have two bars on the top left of your screen.
Also, as it only affects XP from killing, if you are leveling mainly from quests you will never see a difference anyway.
So my opinion is to go ahead and game, and just take the rest bonus when you happen to have it as a lucky break.
Since most rage abilities take 10-15 rage, this means that you should be able to perform an average of 4-5 special moves in a single encounter.