If exporting images for backup, to reimport into a clean aperture or other program, is it best to use 72 dpi or 300 dpi, or does it matter?

Question

If exporting images for backup, to reimport into a clean aperture or other program, is it better to use 72 dpi or 300 dpi, or does it matter?  I want the best quality for any future unforeseen use. 

Answer 1

I am somewhat reluctant to answer your questions after Frank Caggiano's excellent advice, but I really do not like to leave the question open, for there will be many occasions when you will need to export images and to understand how it works.
But please, follow Frank's advice, right now you do not need to worry about pixels and dpi. That is exactly what I meant, when I suggested to you to make sure you keep a copy of your Aperture Library and to back it up with all your other data, before you erase your disk for a clean reinstall.
DPI revisited:
So, is the dpi setting only for exporting to print?
The dpi settings are necessary to define the size of a digital image, since pixels don't have any dimensions. And since you cannot print or display an image without knowing its width and height, you will need to specify dpi when you are printing or scanning.
If I leave it at the default 72dpi will there be any problems getting quality prints in the future from jpeg versions exported with that setting?
Not if you export with the original size - the maximum number of pixels available. That will ensure the maximum print quality.
The dpi settings are required to export versions; versions are derived from the masters and new image files are computed. When you export masters you get a copy of the original file that already may have a dpi setting.
If I choose "export masters", will aperture will export my masters just as they are? 
yes, and  you may add IPICT data if you choose
Pardon my thick skull--I'm an old dog trying to learn new tricks in this digital world!
No apologies necessary, we were all beginners once
Here is another example, maybe that helps a little:
I exported an image (jpeg) with three different setting: export masters, a version with 72dpi, a version with 300dpi and inspected the files in Graphic Converter:
The master was exported like this:
Notice, the master had already dpi settings, although I did not specify any on export.
The size is 51,48 cm x 38,61 cm.
The 72 dpi Version has larger dimensions, but also 10 Megapixels.
and here the 300 dpi version: smaller dimensions, same amount of pixels.