Cabling Question -Only One Prong of Spade is Contacting Terminal.

Actually I ran my Magnepan speakers just like that for years....
Dont worry, just enjoy the music!

I have used that method previously, and whatever degradation in sound, it was so slight as to be negligible, if audible. 

Watch out how vigorously you cinch down on the spade, because you could bend/compromise it. 

It is recommended that you go back in and check the tension a few times, check the tightness.

as this arrangement can loosen more easily than a best fit spade arrangement.

the vibrations and subtle motions can make it so, and will.

So check those connections again, and then do it again about a week later. Just to be sure.

Just..check the security and quality of the connectivity every now and then -- is the byword on this particular methodology of spade application.. 

Essentially, there is enough connectivity for a excellent electrical contact quality..but..not enough friction or frictive area in contact, to ensure a stable connection in the physical realm, in comparison to a properly fit spade.

go bare wire

Get a small chain-saw tooth file the size of the binding post and custom fit the spade?

I'd just shrink wrap the exposed forks to reduce calamity possibilities.

Helpful input.  That resolves the issue for me- I will likely leave it for now. I have a number of other projects that can use my attention. 

As long as the free fork portion of the spade is sticking out to the outer side of both posts and they are tight you should be fine. You could remove the spade and use the bare wire, install a wider spade or use a spade to banana adapter. Over the years I have done all these choices at different times.

Not affect sound quality if there's enough, but yes, preventing shorts is a great reason not to do this.

They do make larger spades as well as bananas.