AbdulAlhazred
Legend
There are a few ways you could interpret Whirling Rend (etc). The attack roll clearly utilizes the main weapon only as that is noted in the Attack: line. When it comes to damage it could be that you use the main weapon's crit for both, the secondary weapon's crit for the secondary damage, or the secondary is simply a damage bonus which doesn't benefit from a crit at all.
Personally I'd favor the second alternative. If you crit with the attack, then the secondary damage is calculated as crit damage with the off-hand weapon.
I'm not sure how Mending Spirit is any better than say if you MCed into Cleric and power swapped in a cleric encounter healing power. There are in any case plenty of ways a character can get encounter healing without even needing to multiclass. Plenty of good items for that.
Personally I'd favor the second alternative. If you crit with the attack, then the secondary damage is calculated as crit damage with the off-hand weapon.
I'm not sure how Mending Spirit is any better than say if you MCed into Cleric and power swapped in a cleric encounter healing power. There are in any case plenty of ways a character can get encounter healing without even needing to multiclass. Plenty of good items for that.