I have an almost comprehensive answer to it (several methods to earn easy exp.). I am sorry that I am late, and still...
First of all, I want to mention that even after 100+ completion of the same task (like speaking for ex.) you still learn something new. This is the same as the usage of language in real life, even after YEARS of saying the same words and phrases again and again, your language skill improves. yet, I agree, that the effectiveness of repetition 100+ times is quite low!
There are several ways to earn experience. I don't care what will you do with this information. This is a complete FAILURE of the Dev Team. And if Duolingo eventually fall and close the project, it means that the Dev team is too weak in comparison to plenty of other projects!
These methods don't include any cheat codes or scripts, etc. There is a bunch of programs for script writing (that may possiably give you much better result) and all of them are prohibited to use. I wouldn't recommend you to do so if you don't want to lose your account due to a permanent ban!
Legit methods:
1) Doesn't require Super Duolingo. You simply add, go through the test and delete the course in your Native language. It gives you 100 exp in approximately 5-10 minutes, depending on the technique and how fast you are. I.e. 1 minute ≈ approx. 10 exp. You may use "Google Translate Extension" (and "Translate the page" right during the test) to make things much easier. My record here is 3.5 mins for exercise, i.e. 1 min ≈ approx. 25-30 exp.
2) Require a lot of Lingots or Super Duolingo. Install "Google Translate Extension". Then complete your Native language ONE TIME with 100% accuracy to get the 17th Unit in the language. Go for the Legendary Trophy in each unit. Using "Translate the page" simply copy and paste what you see on the screen (from the line above) to the form below 
You may use the "ctrl+C" combination and the "Tab" button to make the process faster. My record is 3 minutes ≈ 40 exp. Normal speed is 40 exp = 4-5 minutes. 8-10 exp = 1 minute
17840 gives you 5,440 exp in total.
Yet these are not the fastest ways...
3) THE FASTEST ONE. Requires Super Duolingo. I call it "Pronunciation Drill".
Go to the "Practice" area and click on "Speak" practice in any language you want. You may use your Native or Target Language. I am using a Target Language (TL) because this is also a very good practice.
The Dulingo Practice system can't keep up with what you will be doing, so keep pressing "Enter" (after you done speaking) and then again "Enter" to move to another sentence.
All you need to do, look at the sentence and read it as fast as you can. On the other hand, the Recognition System works perfectly here, so if your pronounciation is correct it will give you a green light in a split seccond (keep pressing Enter all the time). Don't wait while robot read the sentence for you, interrupt and move forward.
My record in here is 25 seconds for the whole exersise. I.e. 1 second give almost 1 point, or 1 min ≈ 40-60 exp.
I.e. it's really to make around 2-3 thousands of exp in 1 hour 
Ocean of exp in no time. No cheating is included. And the 3rd method is highly effective for TLs as well.
L1 
Advanced beginner 
