Professional designers can do it all:
Give slides a professional look
Come up with innovative visualisation concepts that make messages stand out
Use advanced software features to craft technically complex slides
The amateur designer is in a different position and needs to pick her battles. That amazing visual concept of the elephant riding a convertible car does not really work if it does not look picture perfect. That very clever consulting diagram does not really contribute when it actually does not support your message.
You do not need to be a graphics designer to ensure number 1, a decent professional look of your slides. Simple designs can look great (look at Swiss graphic design for example).
When in doubt, drop ambitions on point 2, and 3, and but never compromise on 1. (And this is exactly what SlideMagic is trying to do).