Well, I would think of accessibility as a long-term investment, meaning that it might not instantly attract visitors, but it might make tourists return to the city. We tend to look at accessibility as something only for those with life-long disabilities, but imagine the following scenario. You have been planning a trip for a long time and shortly before it you break your leg. You don't want to cancel the trip, so you travel anyway. Once you get to the city, you can either feel "embraced" by the city for the numerous accessibility features it offers, or you could have a traumatic time because moving around is incredibly hard. In the first case, you will hold a dear memory from the city, recommend it to friends and eventually come back if you can. In the second case, however, you might think twice before recommending the place or thinking about going back there. The same would apply to someone with a life-long disability.
In the end, investment in accessibility is a sign that the city cares not only about the tourists, but also about its citizens.
I do not, but I see it as an extrapolation of what Welch (1995) discusses when explaining Universal Design.
In particular, I believe this excerpt may be useful (although I think you should read the whole text):
"The codes, balancing cost and change, established minimum standards, which provided the most basic access, but did little to encourage designers and building owners to consider the benefits of making buildings more accessible to a broad array of users. Some building owners even wondered why they should make their buildings accessible if people with disabilities never used their buildings, overlooking the paradoxical nature of their question."
Perhaps it would be interesting to consider how, within a city context, space time compression/ accessibility will impact on the delivery of relational good that strengthen the social contract, and in turn impact on the city's tourism economics.