by the very nature of your post, one would assume you care about the appearence of the steps
so, unless its actual teak which is naturally very oily, dont ever leave bare wood on a boat.... it will eventually get water on it and then stain, warp, or splinter and may even split. and the steps are just as likely to get some water on them as the cabin top hand rails.
im not sure what mine has been finished with, but it has a semigloss finish and is something very wear resistant.
judging by the the quality of it and the rest of the interior wood, i believe it is the original finish from when the boat was built in '77...
the finish on the steps is still in great condition (as is the rest of the interior) but they were a bit slippery underfoot when they were wet even though they have traction grooves cut/routered into them (i think the groves are more for asthetics than for traction) and they are especially slippery when you
have only socks on, which is a habit of my wife.
so I used the 1" wide non slip tape as others have. this protects the wood and finish from any damage when my ass hits it immediately after my foot slips on the step, and also minimizes the slippage of my feet (the stumbling is still a problem though, 'specially when capt morgan comes around

)
I would recommend the non aggressive type, which is more rubbery than it is sandy and as ive learned for other applications, the non aggressive tape looks good for a longer period of time in high use areas.