When I was racing there was a number of half wet/dry races and it caused a number of bum clenching moments but few incidents. With the ability to change starting times, good weather reports and decisions an amazing amount of races were run dry. Only 2 races out of about 85 that I started were dreadful and I pulled out.
I was my own master though being a owner rider and could choose unlike a substantial amount of the riders now in teams that have sponsorship commitments. 
The commitment of the riders now to lap at the speeds we thought could never happen is amazing and I fully understand why the no wet races rule is enforced.
There was a ACU statistic some years ago that gave the most dangerous place for motorcycle racing as Redgates corner Donnington in the dry and the safest was the IOM in the wet! 
Thank goodness the TT ended with a full 6 lap senior in great conditions. Its the last bit that gets remembered!