Some 60-65% of accidents are related to approach and landing.
It is not uncommon to add a few knots for Mum and the Kids, but the result is not always what we want. Some actually think it may be 'safer'. In larger a/c it is common to have a max bug speed of Vref + x, which in my experience is often 15kts. To add 15 kts in adverse conditions in a light a/c is I suggest asking for trouble. In adverse conditions such as involving wind then gusts should be considered, but one rule of thumb is half the gust factor up to the placarded Max add on. If not in the AFM then perhaps 10% of Vref may be a suitable add on. In a s/e Cessna for example that might only mean 6 or 8 kts which if greater extends your float and hope distance with the associated risks, such as forcing a touch down or running out of runway. A suitable touch down point should always be selected for every approach regardless of the a/c type. There are always other factors which may have to be considered, but at a particular speed for any a/c it starts to get dangerous. The accident reports show that.