I'd agree with a G-6 it's better than a 4 but the reverse doesn't get to VG-8. It looks lusterless as it is and flat and I know dipping won't help that. It's not bad toning messing up the appearance, it dirt and crud from neglect.
Dipping doesn't help a coin grade better, it just has the possibility of increasing the eye appeal making a coin sell easier than an ugly coin would,,, if it all goes well.
Once the luster is gone it can't come back or be restored. in the end you'd still have a cleaner Good -6.