Well the whole point is I'm just using it for the secondary effects because I use mostly range weapons on this character.
Well the thing is, accuracy (and I think crit?) on your melee weapon doesn't affect your ranged weapon anymore. So apart from evasion or bonus shields, you're not going to be getting any passive benefits from your melee weapon.
However, even a ranged character will get use out of their melee weapon. When you get blinded, or hit with smoke or you're facing an enemy like a cuntsnake with a lot of ranged evasion, you're much better off using melee in those situations. And those enemies that blind/smoke you tend to be shielded human enemies, so you get the full benefit of the vamp blade there.
Afaik the lava saber dot only ticks for a few points of health, I don't think it's very powerful.
I imagine I will be keeping the vamp blade for some time after its damage becomes lackluster.