which items should I upgrade, to get the biggest boost.

If I were in your shoes I'd go for the following items,

3dex 24luk 12atk 1% luk(lv10) luk nose.
epic

2str 2luk 8% luk broken glasses.
epic

13dex 13luk 8atk 8% luk ravenhorn shoulder.
epic

and cube them into unique/legendary tier. What other options do you have besides that branch nose? Are there any 2nd tier face accessories available in kms?