A lot of this does chime with me. I hardly ever went west after dark and never to a bar so don't know about darts leagues. The poverty in the Palestinian camps and the poor Shiite areas around the camps had to be seen to be believed. Beggars abounded at crossroads and they could hire babies for the day in order to tug more heartstrings. They often gave the babies aspirin to keep them quiet though. When I was there there was less conspicuous wealth about, too many armed men with little or no structure to answer to who could take what they wanted when they wanted.I went to Beirut a few times in 1975, just before it went really tits up. I worked in KSA three weeks on/one off and the company paid for an air ticket to Beirut (or the cash towards somewhere further). I was scouting out a place for me and Mrs TS1 to live in (but decided to live in Athens instead, which was a wise decision as it turned out).
I have fond memories of the place but could see many signs of what was to come.
A few things which might strike a chord (in no particular order):
Taxis: All of them were black Mercs. I got lost once and asked a copper where Hamra was. He said "quel hotel" and I replied Hotel Pavilion, Hamra. He stopped a taxi, chucked the bloke in the passenger seat into the back (all taxis were shared, more like a minibus service than a personal taxi), told the driver where to take me and said "Only pay him 5 livres no matter what he says". When I got there the driver moaned like a bastard but I told him I didn't speak Arabic, gave him a fiver and walked off.
Police: I was out for a walk and ended up in a dubious area. I walked past a police station and a couple of cops fell in step behind me. Both carried SMGs. I thought WTF but they merely followed me out of the rough bit onto the Corniche where they left me. I realised that for the first (and only) time in my life I had an armed escort.
Wealth/Poverty. I saw four glamourous youngsters in a convertible Rolls Royce whilst by the side of the road a ragged looking woman was breastfeeding a baby. The contrast didn't bode well for the future.
The British: I don't know what it was like when you were there but there was a very thriving British community there in the mid-70s. There were enough "British" pubs to actually have a darts league and cricket teams. I guess they didn't last much into 1976.
I will add a few more observations later.