Ask a Thief Thread.

NL get a tad better after revamp, but is still on the lower end of the thief ladder. NW have not been revamped yet, so noone can help you there.
As for gears and stars... More stats/attack/power is always better, it is not like good gear is a waste on a class just because it is not top tier. Upgrading from Ilbis/Wabis to Cilibis or BF stars is a waste of funds unless everything else is finished, but if you have the coinage for the White Gold stars even though the scrolls in there are pretty epic, then go for those since they look great.
If you are one of those that jump on the current top tier classes just because, then no, NL's will not float your boat. NW's might, since the trend is OP at release, then nerfed down alot.

NLs aren't really on the lower end of thief classes IMO. I think Shad/DB/NL are pretty much on even grounds right now, until DBs get their revamp. NLs I know for sure are way better than both Shad and DB combined for Gollux, and mob control in general.

Also, as far as Cygnus Knights being OP goes, only 1/3 of the revamps were really OP status so far.