The high fuel surcharges make awards in economy not very economical on most airlines, save for getting an award on U.S. based carriers through their own programs.
Upgrades on TK are more expensive than a round-trip award ticket in business and you need to buy at least a higher mid-range fare.
Europe to Africa 1 is 20.000 miles in economy and only 25.000 miles in business. Just 5.000 miles more. Getting on flights that have the real business class seat is a great value for your miles and money.
TK's best deals however are long haul business awards. 70.000 miles to North America and Asia, 85.000 miles to Sao Paulo or Buenos Aires.
Should you plan a trip to one of these regions, it might be worth saving the miles until you have enough.
On the other hand my feeling tells me that TK will soon increase the required miles. That is why I spend my miles once I have enough for my desired award.