I've driven opened top cars roof down for 5 decades, often in the rain and even snow, and much depends upon what speed and road/journey you are undertaking as to how wet you become. Yes you can find the right speed that the rain flows over the top of you.
However, I find in heavy rain the spray and wash from other vehicles (especially at speed and in particular with lorries) can be quite daunting to travel through roof down and can overwhelm your side screens etc as you travel thru the spray and you get drenched. But more importantly you can for a few seconds loose sight of the road ahead whilst travelling thru the spray and whilst trying to cope with all the water deposited on you, your passenger and of course your visibility thru the inside of the screen. If you do enjoy driving thru the rain make sure you have a leather chamois to hand to clean/dry the inside of your windscreen and side screens, of the water that will be deposited on them, not just by the rain but also the spray of other vehicles.
.Been there, done it and got the medal and from time to time have later wondered why as to whether what seemed a good idea at the time, wasn't that clever or as enjoyable as I thought it would be.
