What benefit do bullet plugs add to ICs?

Plastic has a totally different resonance signature then metal. It is far easier to tune a metal RCA to the wire harness than plastic one.

Some folks like these plugs especially for DIY projects. The plastic housing does affect the sound (dielectric absorption).
Yet metal plugs have their character so it depends on the user. I still like metal plugs. The Cardas GRMO comes to mind.

You have to be very careful when soldering the wires onto the Bullet Plugs. The plastic melts very easily and if you do a little too much heat or too long, you melt the plastic. They also have a very poor strain relief system. I thought the sound was ok, but a pain in the ass to work with.

I have found that the Eichs are the easiest Plugs thus far to work with,but like others here I do think the plug has to be mated with certain types of wire to sound best.

I was really surprised to find that I liked the sound of the Dayton WBT knockoffs. I will try Homegrowns plugs next.

The worst sounding Plug I tried is the Cardas SLVRs. They had the slowest and grainiest signature I have encounterd when mated with Silver wire. I had hoped and thought they would be the fastest and clearest,but the Daytons did what I thought the Cardas would at below half the price.Blew me away!

JMO

I tried them and absolutely hated them. They made the highs shrill. Of all the tweaks that I"ve tried, they had the greatest impact. It was immediate. The sound was more detailed but the bass was reduced. I've seen that trick used before in amplifiers. I spoke with a well known cable company and was told that you can get the same effect by opening up the barrel of a locking interconnect. Reducing the ground contact has the effect of reducing the bass. With the bass reduced, you do hear more treble and midrange detail. It's a change that clearly audible. If you have a speaker that is dark and tilted toward the bass end, I could see where they could help in such a case. Otherwise, I'd say stick with the metal RCA's.