upgrading your arsenic is good for this deck. (you gain +2 dmg each, gets you over some shields)
upgrading the pillars: always a huge boost to early quantagain gain. rushdecks like this speed up alot with towers. if you can, do it.
upgrading the poison: woudnt be my first choise. you gain +1(unstoppable) dmg, but it the costs increase +1. with pillars i would stay to unupped poisons.
next to go:
towers: add a few (or all) the deck will perform better. for a ai3 deck i recommend to split your pillars with pendulums (earthquacke protection).
creatures: i would take a closer look to Flesh Recluse (
http://elementswiki.co.cc/cards-death/flesh-spider-flesh-recluse/). for only 3 quanta you get some nice dmg dealers.
mummys: they cost -1 quantum upped, same dmg/hp. not a big priority.
bone wall: if you go for ai3's you wont even need them. replace them. if not -2 quantum cost is worth a upgrade (also a nice shield overall)
dragons: no - never - really not worth it (except you like the grafic).