OK, so with the caveat of course that "Medieval" is a period that spans 1000 years, and "Europe" is an entire continent, let's take a look at property values in post-conquest England. To be sure, being inside or outside of a walled city or town correlated with wealth and social standing, and any municipality with a wall, "the greatest concentrations of most abject poor" was almost certainly going to be out outside of it, although by no means were they restricted there. When looking strictly at the poor, those on the 'outside' tilted more heavily towards the absolute worst off. Those with no real employment, persons with disabilities, and other sorts who lived off the charity of those willing to give alms, would generally make up this group. Conversely though, those outside the city walls would also be the super wealthy, the landed gentry who didn't engage in day-to-day business, and wanted little to do with the hustle and bustle of town/city life. In places where the walls extended far from the town center, this would mean building their estate on the outskirts of the walled-in part, but many would be on land beyond the walls. So in short, we see those outside the walls being either the poorest, or the richest* people in the area.

Rather than the walls, if we are looking at locational factors, the real driving force of property value in an English town was instead closeness to the city center, and being near the major streets. Within the walls, we don't see too much division of "rich" and "poor" areas, at least on a large scale, and instead the town would be what Keene describes as "a characteristically mixed social environment [...] in which the rich never lived more than a few paces from their poorer neighbours". The well off who did engage in day-to-day business desired proximity to where business was done, generally the town center, but likewise the working poor also wished to be near-by for the very same reason, as they do would be engaged in their trade there, even if for much lower stakes. As such, the highest property values would be based on proximity to the town center, and further dictated by the being near the main streets of the town, although set back to give the residents privacy, with the actual street frontage being given to storefronts and smaller houses, for the lower tier residents who couldn't afford the peace and quiet. Then smaller alleys and lanes splintering off would provide the living space for the lowest tier of working poor, where they were crammed into small, substandard houses built by the bushel, only a short walk away from their place of work - and wealthier neighbors - but out of sight, out of mind, and often out of the sun, in the dark, cramped back streets.

So to sum it up, being within the walls mattered, but it wasn't the walls themselves driving that, it was proximity to the city center that did. The town market and other places of business were something that people desired to be near. The lowest of the low did often live outside the city walls, where land was cheap, but the aristocracy also desired to built their large estates in the suburbs of the town, to avoid the hustle, bustle, noise, and stink.

All info cited from Keene Derek. The property market in English towns, A.D. 1100-1600. In: D'une ville à l'autre. Structures matérielles etorganisation de l'espace dans les villes européennes (XIIIe-XVIe siècle) Actes du colloque de Rome (1er-4 décembre 1986) Rome : École Française de Rome, 1989. pp. 201-226. (Publications de l'École française de Rome, 122); http://www.persee.fr/doc/efr_0000-0000_1989_act_122_1_4595

Follow on question, what are some good sources for historical property values? I would assume that sources are generally localized temporally and geographically, but if there's any more comprehensive research that would be fascinating to look at.