I had 3 SGL with Babylon in my first Epic Game. Later on with the spanish I got only one, in modern age.
Given there are 84 techs to discover, with a scientific civ the max number of SGL you can reasonably hope for is around 10, and you have a 0,6% chance, supposing you're the first to discover all 84 techs, which of course is not possible since all civs start with 2 techs at the beginning. Getting two is normal, I'd say. That is, given getting a SGL is luck, you're normally lucky
Let's say you have quite a good game and are the first to discover 60 techs, you only have around 20% chance of getting 2 SGL.
EDIT : to make it short, the SGL generation is designed so that you will normally get 2-3 in a game for scientific, 1-2 for non-scientific. end Edit.
The thing to remember is : the time of rushbuilding every wonder is over. You can plan for 2 wonders at most, I'd say. But the good thing is that you can have several SGL at the same time, meaning you really can just put them in your capitol and wait for Hoover Dam. It's not like MGL where you must use them fast if you want to get some more