I don't live in a hot area (actually the opposite: Canada) but 59C is pretty warm. Any higher and I wouldn't trust it. I would say purchase the new heatsink. It can only improve cooling. 3.2GHz probably won't require any voltage increase so that means not too much more heat. I can't guarantee anything though.
Personally though, I don't think the cost of getting a new heatsink is worth the performance increase gained from an overclock to 3.2GHz (this is based on the prices where I am which is about $30-40 for a good quality heatsink)