since i am downtown every day and most every night i can tell you that is is very safe. in fact it is the safest district in the city. i love walking down there at night.
as for the riverwalk, it isn't clear what is there. the tunnel entrance is very non-descript and the iron gates aren't very inviting, plus i have gone sometimes when the gates are locked and others when they are open and for the most part there is no rhyme or reason to it.
i have also heard people say it is also a long walk down the tunnel and for the average person (the ones that sit in the lane at walmart waiting for 20 minutes to get a space up front) the walk is even longer. maybe we could "embrace" the riverfront with a parking deck that will loom over it. all in the name of convenience. perhaps we can install escalators and moving sidewalks too, and best of all we could put a green roof on it.