My bad. Sorry for coming over all egotistical, only noticed dagger skills mentioned so far, but even still it's an easy thing to test for isn't it. Nukes are +20 attribute by default so just use the magic damage formula with a 300 attribute weapon to work out if it allows you to have the full 98% bonus or an 8% bonus and whether you need to enchant element to unlock the full attribute, if no, then power. Fluctuation isn't that big so it should be an open and shut case. You're getting a 19% improvement (roughly) in damage if you're still hitting the 150 breakpoint between a +0 and +10 power nuke. I was going to say there could still be a case for +element to shine in full buffed if it's going to make the difference between a 85 breakpoint and 150, but with nuke and seed you're getting 340 att, they can't reduce that even with poe/respot/song and a gear piece.
As for power and duel, pretty sure it doesn't increase base power of the nuke and just increases the amount by a fixed amount / % similar to noble bonus etc.