[Fatt_Shade]

Ofc it pays off. I`ll give you numbers from impossible diff lvl : 31 lvl is 1150000 exp points , all quests give you around 200k exp , darion (including western islands) dwarf lands (all mines) have 200-250k exp , demonis + undead lands have less battles then first 3 locations of games but have 500-550 exp , in the end orc lands are around 150k exp.
I did this with learning lvl 3 asap and finished with 1300000exp, so in all battles 1,1 mill exp without learning i would go at 900k at most, 200k exp less then without bonus exp skill.
Now 30 lvl hero is at 600k exp, 31 on 1,15mill exp so those 250k less from wont mean much at end of game but that is just at almost last part (orc lands) so you play 90% of game with great bonus 20% more exp and those will give you lvl earlier but in the end if you manage 30th lvl bonus stop being important, but all the way till then is great bonus. All bonus from this skill should be 2 more lvl`s throughtout all game so investing 26runes for 3rd lvl skill, to get some 15-20 runes from those 2 more lvls and bonuse on lvlup lds/att/def/int/rage/mana, and that you cant buy permanently. And high lvl bonuses are much better then early, on 28-29-30 lvl bonuses are +3/4 on stats ,or +10/15 rage/mana which is better then bonus from lets say bonus from 2 to 3 lvl of heroism
So in the end i suggest to get learning soon , it will payoff during game.