pets are worth it, yes. in the CS shop, marbas pet is probably the best for PvE, since it gives a massive damage boost, albeit at a high CD. for a witch, any pet that gives INT should be fine as well. sleighing jimmy is also a good choice for magic types, but it's rather expensive in the AH since you can't get it from lost treasures anymore.
blue equipment give colored cube fragments. for the most part, towers give a pretty ok amount of blues after completion. just grind them at a high lvl disassembler for a higher chance of crits