I sailed there a few times in the early 90's, launched from the picnic area/boat ramp (Hay's Landing?) on the eastern side. From memory it was a bit on the gusty side for SE'ly.
Westerlies are gusty anyway on the coast so I would suspect the eastern side of Wivenhoe may be as good as, say Wello, for such conditions.
Hadn't considered again since low dam water levels for some time, but did actually think about it again last year. I reckon I will give it a go this year.
Dinghies and cats sail there regularly:-
http://www.qld.yachting.org.au/db/clubdisplay.asp?ID=4006 www.bvsc.yachting.org.au/