I'm no expert in metering. You've obviously been every comfortable with the meter in the Nikon for quite awhile and find it easy to use. New gear may make your work better, it may not, depending on what you're really trying to do in LF. According to the testimony from the much more experienced and skilled folks who have contributed to this thread already, it can certainly make your metering in any given shot more precise. Do you feel you need more precision?
Some simple questions you may want to think about:
1. If you do buy a new meter, will you continue to want the Nikon with you anyway?
2. Do you find yourself shooting the scene with the Nikon when you begin to meter? I always shoot a few frames in 35 as a sort of reference. I don't hike very far with the 4x5 and having a 35 handy isn't a problem for me.
3. Will the familiar tool, the Nikon, actually distract you from the very different experience of working with the 4x5? I sometimes find it difficult to shift mental modes when changing formats and gear in the field.