What is the general consensus on adding gymnema sylvestre to my daily regimen? Will it have a positive effect on my partially controlled diabetes?

Maybe. There is some evidence that gymnema may help in type 2 diabetes by increasing Insulin secretion by the pancreas and stimulating insulin-dependent metabolism. As with all medications for your diabetes, monitor your blood sugar carefully to avoid hypoglycemia (which is possible on gymnema as well) and inform your doctor so he/she can help with your treatment accordingly.
No consensus. There are only a few small studies and animal studies of variable quality that suggest possible weight benefits. At this point, too soon to say anything definitive. My opinion is that there is no "magic bullet" that will ever be found. Stick with tried and true portion control and exercise.