Playing Guttersnipe and Young Pyromancer is a balancing act. They're creatures, but they prefer if your deck has more instants and sorceries otherwise they're under utilized.

That's not necessarily true. That's a total of 16 mainboard i/s cards, with a multitude of others sided, and considering the lower cost of them all it means that they work well to control the field while pinging my opponent and getting me the little poopers from Pyromancer. Then you combine it with the low cost creatures (which have low power threshold) to mean that I can more often than not be able to attack clearly. You should try it out first. You should see that there is no problem with picking up and pinging to death your opponent.

-1 Magma Jet

-4 Nykthos

+2 Mutavault

-2 Hammer of Purphotos

+2 Fanatic of Mogis

+2 Rakdos Cackler

-2 Anger the Gods

+2 Lightning Strike

+1 Ash Zealot

-1 Purphoros

-2 Stormbreath Dragon

-2 Ember Swallower

+4 Firedrinker Satyr

Hope I helped