imho, if I had 2 extra weeks, I would stay in Morocco. I can understand why people would want to go to Dakar, and mostly it's the same reason they want to go to the north cape or Timbouctou, because of the mythology. But truth is, there is not that much to see, and even the road up to these places aren't the nicest. Morocco has it all and is a much more a bikers paradise than Mauritania or Senegal.
Logistic problems: it's all tarmac, but from Morocco it's 2500 km down one road to the border of Senegal, which is prety boring. Then you will have the pleasure to deal with one of the worst borders in Africa, Rosso, or you can take the detour to Diama.
When you get to Dakar, you will see it's a big dirty and congested city.
On the plus side: you would have an oportunity to get a glimpse of the real Africans, but 2 weeks will have you rush in and out.
But hey, this is just my opinion, lots of people do this 'adventure' every year and have lots of fun.
Here is my video on the long road from Morocco to Mauritania
WestAfricaMovie part2 - YouTube