Ok, so Im shooting a Nikon D-300 with a standard 30-300 optical zoom. It does what I need it to do for when I shoot weddings.
However, I am looking into purchasing a backup for my d-300. Would anyone recommend a second Nikon? I allready own the
D-70 as well as the old as dirt D-100.

Do you mean the Nikkor 70-300mm f/4.5 - 5.6G IF-ED ?
I think you should buy yourself some nice lenses before getting a new body especially when you are shooting weddings the narrow maximum aperture of that lens isn't enough to separate object from the background.
I believe for a wedding the Nikkor 24-70mm f/2.8G ED would be perfect

Yeah, add glass not bodies to your arsenal. 24-70 f/2.8 ed would be sexy... Also the I wanna say, 135mm f/2.0 DC ?, would be a great portrait lens to get.

Brothers, I honestly did not think to dd more glass to it. Hoestly im just shooting the weddings as practice.
I mostly do videography and audio ect, but im getting better in the photography area.

Lenses > Camera. As mentioned in the previous post, you can do 24/70 f2.8 as the ONLY lens to take pictures with in a wedding. I've done it myself. Then again, I've also done it with a 70-200 2.8 and a 100 mm 2.8. Using a single ackward lens for a whole wedding = as tough as Navy Seal training

Also, because you aren't shooting full frame... If you don't plan on getting a full frame body sometime in the future... Another great lens to consider would be the 17-55 2.8, but keep in mind it is a dx lens and if you ever upgraded to full frame it wouldn't work on that body. But I know several people that shoot w/ that lens for weddings. Very versatile for that type of work.

Personally, the D300 with 17-55mm f/2.8 and 70-200mm f/2.8 is the best DX setup for weddings....but don't forget flashes and softboxes are just as important.
My new favorite lens has been the 85mm f/1.4 ... I've been going out of my way to use this lens as its incredibly sharp.

There is no reason to get another body if you've already got a D70 and D100. They will work fine as backup cameras.