I've flown that route many times on Delta, and it's one of the ONLY first class cabins with lie flat seats in first class. It is a very hard one to upgrade to first on, and honestly it's the return flight that it would be best for (since it's overnight). I used to be able to use miles for these seats, but it's gotten harder and harder to use any amount of miles for this route in first (and last time we did coach, ugh, which cost us as many miles as we used to get first for!).
I'd say going over, comfort plus is nice with more leg room. It's roughly $150 per person for that length of flight.
If you can snag first coming home, take it. It may cost quite a bit, though, and these seats fill up since they're more comfortable for sleeping.
The only other current route with these type of seats are AA out of DFW that I'm aware of. We go to Hawaii a lot from the East Coast.
Once I was offered an upgrade for the kids and me and the kiosk from Chicago to HNL on AA (back when that route also had lie flat seats). It was $400 per person, and I took it. Yes, $1200 but our tickets were free using miles so I justified it that way. Return we checked in super early at HNL but no upgrades were offered - they rarely are on the return flights.
I would say to expect at least $400 or $500 to upgrade this flight if you're lucky to get it.