I'm looking forward to this "synergy" system: most of the upgrades and buildings are noob-trap money sinks (especially since most of them have higher cost than oil rigs past 300 or so). I would love for the optimal strategy to not be "ignore everything that doesn't benefit oil rigs."
If any of you are having difficulties beating Hard... I just beat it with 7 axe throwers and 1 wand guy. Build the wand first, and upgrade it to about rank 2 in everything but speed, then keep adding on axe throwers and upgrading them to rank 2 in all but speed. Once you have max, upgrade 1 at a time to max rank in all stats (cept speed of course). Use slow and poison mines on bosses if you have to.
Alternatively, you can just send me a PM.