+4% isnt that great :X Waste of a title imo. but thats just me.
For high levels, +4% is the best damage title available. Effort-wise it may not be worth it, but Shock is already a good skill on it's own so it's win-win.
As for comparing it to Heat Buster, you can't really compare a passive skill like Shock to an active attack like that. Since you can use them together, although Shock seems to benefit Melee more than any other type (Range/Magic/Alchemy can easily hit aggressive mobs, the same doesn't apply to melee).
Damage-wise, you'd probably be better off doing Shock+Smash than Shock+Heat Buster, especially since you need to charge up Heat Buster with other weak skills while you could just spam Smash/Magnum/Blaze repeatedly. Not to mention the fact that Heat Buster is the weakest out of the 4 mentioned skills.