At least for the suggestion forum I think this would be quiet cool.
1. Some people missclick and vote the wrong choice.
2. People didn't understand a suggestion at first and vote quickly, after reading correctly they'd change their mind.
3. Many suggestions are updated frequently, you can turn a stupid suggestion into a really great one. So people might change their mind.
Most suggestions don't have many voters and therefore even a "missclick" vote can e.g. prevent a suggestion to move to Tier 1.
Just a thought.
Restrict it to just the public votes imo.
Private ones shouldn't be change-able, as with the large sticky threads for alt avatar votings and stuff like that, might be abused.