I thought Friend Safari was cute and had some point to it since you could get version exclusive and hidden ability pokemon + the odds of encountering a shiny pokemon were so high-- once in a fire safari I ran into a shiny Ponyta purely by accident as I stepped on the first tile of grass.
The dexnav in Oras objectively is a better, more advanced version of Friend Safari because it has all off the same perks of friend safari, but way more pokemon, and the pokemon there could also carry egg moves you would normally have to breed for, and potentially appear at much higher levels than the set level 30 of Friend Safari. However, I still liked Friend Safari because of it's randomness-- it's fun and mysterious not knowing what pokemon are going to be there. It's also really easy to use. Whereas you can accidentally break a chain with the poke radar or the dexnav, you never have to worry about that with Friend Safari. You just walk around in the grass until you see what you are looking for. I caught a lot of nice shiny pokemon this way like Trapinch for a flygon, a Swirlix who is now a Slurpuff, Dedenne, Pikachu, Butterfree and a Pyroar. So I really appreciated the friend safari feature as a player with fledgling skills.
You do have to have a lot of different friends to make it worthwhile since there are only 3 Pokemon in every safari, and only 2 can be unlocked If your friend hasn't beaten the game or is not online at the same time you are playing. I didn't really mind the part of only being able to get a set few pokemon from someone else's safari though because I have many friends fortunately. I happen to really like trading and meeting new people, so there were a ton of safaris ready and waiting for me to explore when I first tried it. You also do get somewhat of a break since not every friend has to have traded or battled with you or even needs a Pokemon game, any friend registered was good.
I also think that if Friend Safari contained many more Pokemon it would just be too easy. It would give you less incentive to keep trading with different people, and decrease the rarity of finding a really prized pokemon because your odds would just be higher of running into it the more species of Pokemon live in one safari. It makes getting a safari with a Pokemon you really like not as special. One other advantage of having only 2-3 Pokemon is that you could target faster the Pokemon you entered to get compared to say a wild area where a dozen different mons might live.
The only thing that annoys me about Friend Safari is that you have to coordinate to be online at the same time with your friend just to unlock the third pokemon species and the hidden abilities, that's unnecessarily burdensome.
Also it is possible for friends to have not only the same type of safari, but the exact same set of pokemon on the safari. I had two friends on my 3ds who both had the exact same 3 ghost Pokemon on their safari, and others that had 1 or 2 of the same pokemon. it's disappointing when that happens, because you're not being offered much or anything new despite them being different people, but all and all I do think Friend Safari is kinda cool, and I would love to see this feature revamped and made better than before in a Pokemon XY remake.