Hi a.12912,
This is my first post on this site, so maybe wait till more reply to your questions, but here's my 2 cents worth...
I bought my e30 318is a few months ago and noticed temp gauge only just got out of the blue zone in normal driving , but temp would creep up to half in traffic, and would nudge past half way in really heavy city traffic (giving me the sweats...)
I changed the thermostat for Wahler 88 deg (the old one was 88 deg too, but was sticking open) and flushed the coolant and now it's like a new car, gets up to temp quickly and stays rock solid just below half on the gauge, doesn't budge at 70mph on the motorway or in really heavy traffic.
The fan clutch seems in good order on my car so I'm not much help there, though yours sounds busted, but I'd wager a new 88 stat and fresh coolant would go a long way to solving your problem, btw, the old coolant flushed out of my engine looked clean too, but mustn't have been doing its job if it got past halfway on the gauge before flushing, and now it seems welded to just before half on the gauge
Seems to me your (now broken) water pump may have been on way out anyway if it took a bit of revving to really get the coolant circulating (?) and au300 does seem cheeky for a new one, but BMA Parts in the US have a Meyle one for US$70 (au85 I think), could prob be shipped to Oz for not much more, I have heard Meyle are pretty good, dunno if they're OEM though.
In fact, BMA prices are good enough (and genuine BMW prices cheeky enough) to make me consider shipping over some stuff from there to Ireland, GSF and Halfords here are beyond useless, and I'm far from a pro when it comes to repairs
best of luck anyway
--Neil