We know that whenever a Saiyan is healed from a mortal battle his power level will rise... So i sometimes wondered why they dont just get a handful os senzu beans and just bring themself close to death time and time again and just let their power rise again and again, is there a reason that they dont do this?

They become stronger when they are almost from battle. They have to fight something to get stronger.

@Skunkstein: @Hazlenaut:

They can always spar half to death and ask picollo to heal them

Vegeta did in the Frieza Saga....

Its theorized that the boost they get from near death experiences in battle is an auto evolution mechanism that helps a Sayian reach the SSJ state. It makes sense if you look at the boosts Vegeta and Goku receive after being beaten to near death. Each one is subsequently stronger than the last, making for an exponential curve until they reach the minimum power level needed (probably about 3-3.5 million or so) to ascend to the SSJ state. After that, the boost essentially goes away...