I've worn tanned leather boots for years. About once a month or so I would clean them with some saddle soap or other suitable cleaner then when dry, spray them with silicone boot spray. this method works very well and my boots stay waterproof for years.

Recently, I got some new boots in Black leather. They are in fact military issue infantry boots. I'm wondering about how to care for them. Should I use the same method as above or should I use black shoe polish to keep them looking good? Will the black shoe polish keep the leather's water repelency up to snuff?

polish, polish, polish, polish, polish, ...!

neatsfoot oil

Brother,
I wish I had a dollar for every time I polished a pair of combat boots.
This is how I do it. Get them nice and clean first. I use just plain old Kiwi polish. You can use Parade Gloss if you can find it.
Put on the polish and let it set about 5 minutes before you buff it off. Use a brush for the first couple of coats and them use a soft cotton cloth to buff them with. Once you get a shine then start using a wet cotton ball to get a real spit shine.
It will take you a while to get them looking really good but stay after it and you won't be sorry.

Do you want them to look good or last long.

Neats foot oil, not a lot.

When dirty wash in plain fresh, cold water.

Dry in a cool to cold room.  Fill them with wadded up news paper.  

Let them dry slow.

Add another light coat of Neats foot and then polish if you want.

I dont have a lot of experience but, I have put standard polish on in a thick even coat and then melted it with a lighter and then buffed.  I don't know if it helps the boots last longer or if the shine lasts a long time but it was fast.

When I was 19 I bought my first good quality leather jacket and shortly after that bought myself a new set of motocross boots for the dez.

Up until this time I had never taken care of my dirt bikin' boots, and it showed.  I realized after buying my jacket that good leather is an investment, so I asked the guy who made my jacket what he would recommend as far as maintenance was concerned.

I sponge rinse with lukewarm water, followed by a light application of Lexol leather cleaner and ending with another lukewarm water sponge rinse to get rid of any suds.

Once the leather is clean, I apply Lexol leather conditioner and buff in lightly.  After a few minutes, I buff out the jacket/boots with a clean cotton cloth till I get a nice sheen.

Been doing this since '85, and though I've gone through a few sets of boots, my jacket still looks pretty darn good.

These are the Gore-Tex lined issue boots. Gore-Tex is great but it does leak some if you're standing in water. I find that it really helps if the water has a hard time getting to the gore-tex to begin with. that's why I like to keep the leather treated.

I've never needed to polish a set of brown/tanned leather boots, I've just cleaned and siliconed them.

Does the polish waterproof the leather too or just make them look good?

If water repellancy is what you seek I would strongly recommend Montana Pitch-Blend water repellant leather dressing. All natural to boot and keeps your leather boots looking new. I was turned on to these in a hunters forum--they swear by this stuff and it also doubles as a cover scent during hunting applications. I've had nothing but good experiences with this.