which one? lens or body?

Hi,

I am a proud owner of D5100, my shooting style mostly is on the street and indoor (with no flash) just recently I face problem to obtain decent enough shutter speed, many of my image was taken at ISO 1600 and higher when shooting indoor, and many was having slightly motion blur

my lens currently just a kit lens 18-105,

my question is, do I need to upgrade my lens? or body according to my need of less noise

below are some sample from my shoots

my budget for these (excluding of the sale of my body if necessary) is max USD1000

thanks

Nis Daniel

Iso 1600 1/15 sec

Iso 4500, 1/15sec (grain on the face due to heavy noise)