Peat as a Substrate

With all the talk about differing substrate additives, has anyone considered 
using a Peat / Vermiculite mixture?  These two substances, along with 
composted manure, are the "black gold" of dry land gardening.  From all my 
readings of postings and reference books, its seems the purpose of substrate 
amendments is to contain, in a usable form, those nutrients needed by the 
plant roots.  Since gravel doesn't do this very well, almost any kind of 
amendment (laterite, clay, soil, vermiculite, etc) is an improvement over 
plain gravel.  The addition of undergravel cable heating encourages the 
continuous transfer of nutrients from the water into the soil.  Thus you 
feed the leaves as well as the roots.

I have a 42 gal, Discus community tank, that is heavily planted in plain 
gravel.  I'm setting up a 125 gal in March (b'day present from hubby who 
doesn't like aquaria) and want to use some type of substrate additive. 
 After seeing the cost of laterite (!!!), I'm looking for alternatives.  And 
since it will be a soft, acid water environment and peat is a type of filter 
medium, I'm wondering how it would work as a substrate.