OP - please search as there was just another thread like this somewhere around here. All depends on how much you value those miles. Honestly, if you've never done it, go for F, it's a nice experience and the lounges alone are worth it. But overall, the quality of NH F has gone down over the past 5 years - to give you an idea, I never upgrade to F anymore, and I used to every flight.
But I don't want to be negative. It's a great experience and you should certainly try it if you can part with the miles.
If you want more details on the delta between J and F, let me know. Here's some quick thoughts:
- F menu is radically larger. Quality isn't much higher, but you have many more choices.
- Wine / champagne is superior in F, Krug alone is worth it for those who drink a lot of champagne.
- Seat is much more private in F. Harder to communicate with your girlfriend, and you won't get window seats if you want to be able to even have a chance to talk. The partition between seats comes down, but when sitting / lying down, you can't communicate much. Not a huge issue, just something to be aware of.
- Service is similar, more personal in F.
- Less pax per lavatory, so you'll rarely if ever not find one of the two F lavs open.
- FA's tend to be older and more experienced in F. Sometimes more robotic, but always kind, if not a bit impersonal.
- Pajamas in F are so-so. Sometimes I don't even bother. But it's a nice experience. You can keep them too.
- If F isn't full, they will (upon request) turn down another seat to be your bed, so you effectively get two seats, one for sleeping and one for sitting / eating / normal activities.
Overall like I said before, if this is a once in a lifetime kind of celebration, go for it. Especially if you can find 2 F seats available. Go in with low expectations and you'll be happier. :-)
PS - Interesting avatar name you chose. :-)