If you have a few fans in your fixutre, the outer glass will be only slightly warm to the touch and will not burn you. I would not touch the plasma or bulb or anything - ouch. Go ahead and touch a T5 or LED without a fan.
I hang pendants over my tank with the wire cables - if they do fall in the water, the breaker will blow but the tank will be fine (ask me how I know?). Both the tank and the lights stay cool with some small fans. My 1000W heater does not run for most of the day while the MH is on (it will run a bit, but WAY less) - the lights mostly heat the tank instead. This can save quite a bit of money since tank heaters are no joke. If the temp rose, then this would be an issue, but it doesn't.