I agree that gear swapping in FFXIV isn't really that viable. Like I said in my above post, I have the same problem as your #2 listed problem, which is irritating when it doesn't change back. Still, the bonuses some pieces give are good enough for me to try and make it work.
As for my feelings on being a non-blinking WHM and being able to perform well with Enhancing Magic, it's perfectly viable, and kind of what I recommend and go for myself. It's difficult to really start a set for this without Darklight Gloves at the least though, so start pressuring your Linkshells into running Aurum Vale a lot! Like I said I have 422 Enhancement with my set. I can get 427 with an Amber Ring +1 instead of my Turquoise Ring +1, but I do like my MND bonus I get from the ring. You certainly don't have to be a blinking White Mage to be efficient with enhancing, I just figure since protect is a 5 minute buff, if there's anything that's semi-viable to blink on, it's that.
I would not recommend splitting the 2 WHMs into an Enhancing WHM and a Healing WHM. All WHMs should have a decent Enhancing Magic level because Regen is so important. Communicate with your other WHM and find out if someone has substantially more Enhancing than the other, like for example since I have Darklight gloves and breeches, I have the 2 pieces that boost my enhancing the most, so my buffs are much more potent than another WHMs who does not have this gear. As such I usually let the other WHM know that I'll take Protect and Stoneskin when we stop for buffs, they take Regen and I throw a single target Regen on the tank since mine is more potent.
That being said, in the midst of battle I still let the other WHM do their thing, they can recast protect and Stoneskin and AoE Regen and all that all they want, their stuff is still plenty potent. I tend to stick with healing the tank, since my bonuses to Regen, Protect, and Stoneskin benefit the tank the most, so if you do want to go with an Enhancing Magic build, try and put yourself in the Tank healer's role.