Is it worth going to Central Serengeti in September? Or should I spend more time at Masai Mara?

In fact Masai Mara and Serengeti are one big nature reserve, the first one in Kenya, the second one in Tanzania. If there were no immigration formalities to fulfil, you wouldn't even notice you're in a different country!

If your purpose of the Serengeti during September is for Migration, be aware that the Migration will be in the Masai Mari (Kenya).

That's not to say there aren't other animals to keep your interest in the Serengeti, and in the Western Serengeti there are herds of wildebeest that do not migrate to Kenya.

I gather you'll be in Kenya, so is your consideration of the Central Serengeti part of other areas in Tanzania, the Ngorongoro Crater, or other parks?

Lucretia: Sandi is right. Your best bet in September is the Mara or the far northern Serengeti, in the area of Migration Camp or Kleins Camp. When we were in the Mara two years ago in mid-to-late September, we had the great fortune to see a wildebeest crossing of the Talek River. Of course, as many people will point out, the location of the migration depends on the rains. The difference between the Mara and the Serengeti are the size of the areas, with the Serengeti being the larger of the two.

Lucretia, my wife and I spent 4 days in the Serengeti in Sept 2002, and there was no shortage of animals to see. Lots of lions, wildebeestes, gazelles, etc. But the other posters are correct, if you're looking for the migration, odds are that it will be in the Mara at that time.