It is probably my most favourite wonder, so I will answer
Basically Alexandria is a hit or miss wonder. You can win with 70 points and you can lose with 35 and have no chance.
Alexandria is very strong with resources in all versions. Caravansery as a part of wonder is just great. If you get normal Caravansery in 2nd age, it is perfect. With 2 good brown cards you can build basically everything in 3rd age with not paying at all. The second stage of wonder is not that good, since it gives you glass you do not need. There are no cards with 2 glass costs. 7 points for 3 stones is ok. 7 points for 4 lumber is not, but still playable, given you have 2 caravanseries to use.
And how to win? Well, you have to be a bit lucky. It is a great help to win battles with Alexandria. It is not easy, but it is good. If you rush your 1st stage of wonder, you can build 3 red cards if 1st age which can make your neighbours resign on playing red cards at all.
Blue cards are always good for this wonder, but you can build only Palace + Pantheon in 3rd and it still will be good. You will have resources for that. 15 points for just 2 cards is very good ratio.
So it all comes to 2 things:
a) Being lucky and get useful guilds in right order
b) Somehow get green cards work - Alexandria is not really built for "all green" strategy. It is good for 4 same symbols + guild if possible though. Then I suggest start with Scriptorium, so you waste only 2 cards on this strategy in 3rd age.
But my most favourite strategy is multicolor. Just build 1 row of greens. 1 in 1st age, 1 or 2 in second, 0 or1 in 3rd. It gives 10 points for 3 cards, which is not bad if you spend only 1 card in 3rd age on it. Build some reds ASAP, you do not want to waste your precious 3rd age cards on battles. Build caravansery and arena (+ ludus in new version). Build guilds and make your blue cards strong. This is the way to get around 60 points regulary.
You need to finish your 2nd age with 15+ points. You can get these points from battles, blue or green cards, wonder. If it goes very well, you can start your 3rd age with 25 points! (10 points on greens, 8 on battles, 7 from wonder or blue cards). 25 points is very very very strong position to start on in 3rd age. Considering you can build 6 cards and each card can give you 6-7 points in 3rd otherwise you should not build it. The red cards are tricky, focus on them in first 2 ages so you do not have to spend cards in 3rd age.
Problem is, you have to be a bit lucky with cards and neighbours. Few weak hands in 2nd age and this strategy is doomed. The same in 3rd. Also Rhodos, Gizah or Olympia can make your battles very difficult to win.
Alexandria in any version (new/old, A/B) is challenging, but it is not a bad wonder. I usually play B side in old edition and A side in new edition. Old Babylon is much more difficult. Not even to mention new Olympia, which is definitely the worst wonder of all in both editions.