I wonder if the knowledge gained from the functions of plant-degrading genes can be put to other therapeutic uses in humans. I am thinking of the build-up of cellular rubbish in our cells which is one of the principal causes of ageing. Maybe this could be used to design chemicals or molecules to help us get rid of this rubbish

This is a new twist on the old saw! 

Does anyone really think it's wise to consume your food supply to fuel your car and air condition your home?  Especially since it takes about the same amount of fossil fuel to create the biofuel as it does to make the gasoline, at least for now.  And coal and other carbon based sources of energy are abundant on the planet as is nuclear fuel.  Clean it up, yes, but don't make food supplies your source of power.  That's just crazy and intuitively obvious. We can live without cars and air conditioning but not food.

It seems to me that IF we're looking for a source of genetic materials for the enzymes needed to convert complex starchy materials into simple digested sugars for fermentation may be found in some more exotic parasitic plants found throughout the world. These plants rely on a host plant of course, unlike decaying plant material like Mushrooms and fungi.

UCLA has some decent info: See link
http://www.botgard.ucla.edu/html/botanytextbooks/lifeforms/parasiticplants/index.html

Studying the genetics of algae that can "store" sunlight as lipids would seem to be ever so much more valuable, as compared to familiar agricultural crops.

Alternatively, a method to store sunlight in some mode of electricity.

It would seem simpler and very much more likely to be of greater value to work on certain simple algae.  As opposed to expending much time, money and effort on very much more complicated, if familiar, "crops" that are comparatively much less efficient at storing solar energy.

It seems obvious that using agricultural waste will be more economically viable than competing with food production.  However, all alternative solutions need to compete with existing oil and there are two hurdles involved.  One is competing at the current price of oil (this is not a problem for many new technologies with oil surpassing $50 a barrel), and the other is getting industry to lay out large capital expenditures when faced with the possibility that, as unlikely as it may seem to us today, oil could fall to below $40 a barrel sometime in the future.
One answer is the permanent imposition of a “conditional” tax on oil based fuel.  With the cost of oil over a particular threshold (maybe $40 a barrel) there would be no tax imposed.  However, if the price fell under the threshold, a tax on the fuel at the pump would go into effect and would make it equivalent to the base price.  Industry could then safely invest the billions of dollars necessary to develop bio-fuels, tar sands, coal gasoline or any other rational possibility that works over a certain price.
It wouldn’t hurt either if Congress would give such energy independence providing ideas, some extra tax relief.

So why not choose Kudzu....Anyone who has been in the south knows this plant grows very rapidly.