We have almost exactly the same LL characters outside of my 3rd (Warlock) being 311 but regarding the Nightfall rewards, I've thought recently that somewhat of a solution would be say a choice between either the Armor / Weapon / Class Item / Ghost that drops or 10 Strange Coins. This would at least give you the option of being rewarded with something somewhat useful. They could make it so that you collect rewards (make the choice between gear reward or Strange Coins) from the class Vanguard / Faction (dependent upon the reward) leader just like how some of the quest rewards were handled starting with TTK.
Then again I don't have much use for Strange Coins anymore either. To possibly fix this, they could make it possible (albeit a small chance) to receive Exotics from Xur in the 311-320 LL range once you hit LL 311.
This is a decent idea, but the trade off seems a bit pointless. Basically, if you should just be guaranteed Strange Coins when you are over 300 with an increase in exotic drop chance and decrease in legendary drop chance. It's a weird paradox of reward structure.
Nightfall when you are 290ish or lower: It is much more difficult since you are a much lower light, but most rewards will be at least somewhat useful. However, the problem here is that if an exotic drops it is guaranteed to be 290, thus not really a benefit to your LL.
So in this scenario, Legendaries help with LL, Exotics don't.
Nightfall when you are over 300/305: Legendary drops are basically 3 marks aka pointless. There is a small chance you land something better, but very very small. Fortunately, if you are lucky enough to get an exotic and you are lucky enough to have it roll at 310, it can help with your LL.
In this scenario, very very few Legandaries help with LL while only SOME Exotics help as well
Nightfall when you are over 310: Legendary drops are still garbage. Now Exotics are guaranteed 310, but will (for the most part) not help with LL.
In this final scenario, neither legendaries nor exotics help with LL.
So you are either hoping for legendaries at low levels or hoping for exotics at top levels, but never both at the same time.
It's a sorry state of affairs when the potential engram boss drops are better than the actual nightfall rewards. Popping a 3oC gives you a similar chance at an exotic than running a nightfall does, with the difference being I can run strikes/bosses with zero modifiers. The best thing I got from the nightfall this week were the strike-specific gauntlets, which was a boss drop.
3 weeks back I ran nightfall all 3 times with my characters right at 300. The best drop I got was when I reran it a fourth time using 3oC and got an exotic.
Nightfalls suck. Plain and simple. The only 'weekly' activity worth doing requires you to coordinate 5 other people to party with.