Yeah that's a good question - so a good rule of thumb I use is one Level 50+5 Damage IO gets you to 53%. One Level 53 Damage/Accuracy HO gets you to 38.2% for both. If I'm going to be fighting high level 54+ enemies, I tend to drop Level 50+5 Accuracy IOs in to my -def debuffs and use that instead of missing out on potential Damage/Accuracy boosting HOs in my main attack chain.
Ice Blast is a very proc'able set and coupled with the debuffs from Cold Domination, the player gets a complimentary array of powers for any given situation.
Edit: Oh but to your point, I don't really focus too much on set bonuses in my attacks themselves. I'm usually a 2 HO, 4 Proc kinda player. This is mainly because the non-purple/PvP set bonuses aren't usually worth the trade off in dmg/acc or proc'ability. That's just how I see it though, other folks could be different.