The 35-80 may be worth keeping, particularly if it has the metal mount and not the plastic one. The metal mount version is exceptionally sharp. It will probably blow away your 28-200 at the focal lengths it supports.
The non-Nikon zooms you mention are unlikely to be exceptionally good optically. You might want to look at upgrading them over time. There are lots of good Nikkors out there for not very much money.
A 50/1.8 is cheap, too, and very sharp, and would give you a great low-light solution. The 35/2 is a little more useful but about three times the price.