If there is a specific property that you are interested in and you can confirm it was affected by the 2011 floods get some insurance quotes on the property so you can accurately determine your costs. Not all of Rocklea floods
Haven't followed this area closely, but IMHO it would definitely make a huge difference. But the suburb has a whole carries this stigma, I can remember driving around parts of Archerfield and Acacia Ridge looking at the old 74 flood marks and it was always assumed that to could never happen again due to flood mitigation but that wasn't the case.
If you want to have a gamble, go and throw $50 on red or black at the casino. Spending a few hundred grand on a house in Rocklea is not a calculated risk - Google some of the stories of people who didn't read the fine print in their insurance.