Lightning Bolt is better, but the critical mass of damage provided by Shrapnel Blast is very important. Also, 4 Lightning Bolt increases the deck cost by almost $15, or half the total deck price.

I agree with you on Spell Pierce, and I think I will run 2 each of Spell Pierce and Stubborn Denial.

Serum Visions would be a nice addition, I'll see what I can do to get those.

Master of Etherium is also good, but it won't usually get much bigger than Chief of the Foundry in this deck.

I disagree with you on the Maverick Thopterist vs Whirler Rogue - also, the unblockable ability is helpful.

With not too many big creatures, the Myr Enforcer is a useful addition. Also, having even 3-5 artifacts can make it worth it.

I will look for some Memnites.