It hasn't risen.
The Eurobarometer Interactive search system allows users to create line trends of survey questions over time. One such question is:
Taking everything into consideration, would you say that (your country) "has on balance benefited"/"would benefit" or not from being a member of the EU?
Taking everything into consideration, would you say that (your country) has on balance benefited or not from being a member of the European Union?
European Union (from 03/1983 to 05/2011)
Source: Eurobarometer