On the question of lower level nanocosts:
You will do more damage for the same nano-cost with the new nukes at all levels... or you could see it as being able to do the same damage for much less nanocost by casting them a bit less often...
And you will do more damage per second with the new nukes at all levels as well... and be able to cast other nanos while doing that.... either more nukes for even more dps... or debuffs/pet buffs etc.
Frigid Blast used to do 1.45 minimum damage per nano-point. New Frigid Blast (now Wintery Bayonet) does 2.0 min damage per nano-point. 37% more damage per point of nano spent.
Mind Howl used to do 1.36 min damage per nano-point. New Mind Howl does 1.66 min damage per nano-point. 22% more damage per point of nano spent.
Frigid Blast used to do min damage of 160 and at that level, with a casting time of 3.45 could be cast at best every 2 seconds = 80 dps. Probably a fair bit slower in most situations. Wintery Bayonet does 608 min damage every 4 secs = 152 dps and with a 1s attack time will be instacast in most situations at its level. So at least 90% more dps - while giving 37% more damage per nano point spent.
And because you can cast other stuff in between the new nukes (because the cool-down is longer than the recharge) - you can maintain that 95% more dps - while also casting other nanos - e.g. debuffs... but on the old nukes, you had to use all of your casting time to maintain far less dps.
Old Mind Howl optimistically did 118.5 dps whereas New Mind Howl does 165.5 dps.... and leaves you time to cast other stuff while doing that.
As far as I can tell by scanning them by eye, these results basically hold through both lines.
X