In defense of the Obelisk/Madrassa (which I consider top-tier UBs):
The main use of these (which justifies them on their own, I feel) is that they can be used to lightbulb Theology very early. You're almost guaranteed Christianity if you want it, and just as importantly you get Theocracy for some serious extra power in early warfare (and as Spiritual civs, you can leveage that very well). Plus you get first crack at the Apostolic Palace if you want it, it makes a good tech for trading to others in your religion, and if circumstances are right, it lets you go straight to Paper for Sankore or delay Civil Service outright on a quick run to Liberalism.
If you're very good (or lucky) with your timing, a second prophet can actually be used to bulb most of Civil Service too.
The next use is that it can beome VERY difficult to generate a prophet after about your third or fourth GP, which presents a problem if you want a shrine in the mid-to-late game (eg Taoism/Islam or a captured Holy City). Two extra prophets allowed can help a lot with this.
Third, if you build Angkor Wat, you can run priests like engineers and get a nice hammer bonus.
Fourth, if you're not totally picky about what GP you generate, you can have 4 instead of 2 specialists in a city before CoL, and thus generate GPs faster. Great for a second GP, where you can potentially bulb either Philosophy or Civil Service as soon as you reach CoL.
Fifth, the Madrassa gives +4 culture, which can let you settle close to enemy civs and win the border wars, and can be worth chopping in straight away without bothering about a monument.
The Dun is also great - fast-moving, hill-attack-bonus, 50% withdrawal longbows and crossbows are very nice to have, especially teamed up with the Gallic.
The worst for me is the Salon, because I never play culture games and I don't want my GP pools polluted with filthy artists. I understand how it's good for others though