In terms of raw GPT saved, they dont match Inca, China, Egypt or Songhai, but they do get extra luxuries from the bazaar to sell, and those make a lot of gold.
IMO the larger the map and the more opponents, the stronger Arabia becomes. Prioritize settling every city near luxuries, and research to currency for the UB, and the amount of gold that Inca save on their cheap roads is easily beaten by a single luxury trade to the AI.
I remember thinking, and people suggesting to buff their UA to +2 gold per trade route, but that would overpower them giving them the same amount of raw gold bonuses / savings as other civs on top of the extra luxuries. You also get double oil which is very useful, if you dont need it, again you can sell it!
Overall while the +1 gold per route doesnt seem too good at first glance, thats because you overlook how much money trading makes.