Here's an update. I've recently put together a regular routine for my feet to keep the cracked/dry heels at bay.
1. wash feet, then soak in whatever, but thoroughly soak. I like to add herb-infused water to my foot bath.
2. exfoliate with a sugar, not salt scrub (salt stings cracked heels) & really work on the heels. Rinse well to get all the scrub off
3. cover heels with salve. I've tweaked my salve to use fractionated coconut oil which absorbs really, really quickly, one other liquid oil (your choice), jojoba, tea tree EO & lavender EO for their antibacterial & healing properties
4. cover feet with socks
Done once a week until heels are healed, then once every couple or 3 weeks to maintain.
Sometimes really badly cracked heels can be caused by a fungal infection. That should be treated first.
My heels are as soft as a babies. Whenever I feel the slightest bit of roughness, I use the exfoliating scrub right away followed by the salve. Right now, I only need to exfoliate about once a month, but I moisturize with a thick cream at least once a day, twice if I've done the scrub.
Maintenance is really the key here.