A word of advice: Don't argue with veteran players, they will win. But hey, at least they aren't mean about it
As far as refineries go, they are useful if you have a good planet with plenty of lanes to other mineral-rich worlds, or becuase they are the only way (other than research) to increase metal and crystal income.
If any of you have played supcom, i use refineries like mass storage, to increase income.
If there isn't a good place to set up a refinery, i usually neglect them until late game when expansion is more difficult.
So to answer the "worthless or critical" question, it depends. Much like trade ports, there is a time and place to use them. If you spend your time setting up a trade netwrok on a map like quick strike or close encounters... you will lose.
But if you use trade on larger maps and your opponent doesn't, you will win.
Refineries aren't as effective as trade ports because you cannot make a chain of them, but still, they remain the only way (other than research) to increase the amount of metal or crystal you can get from your existing extractors
