--- Begin quote from "Melon"
The regular game and NG+ share the same party, so you can swap between them at any time and carry over all XP/scrap/items. NG+ is a significant step up in difficulty at places so if you're struggling I'd advise going back and beating some of the higher difficulties on the regular game first.
--- End quote
Doing the last level on Casual difficulty with 300% XP/Scrap gain is a very good way to get lots of stuff (specially Scrap).