I take "character" to be suggestive of something out of the ordinary, unique, and specific to a location or building. Replacing much of this stretch of McGrath with newer, cleaner, better maintained developments will no doubt be welcomed by many, if not most, who live and work or even pass through the area, but there's no question that a set of vanilla, by-the-numbers, "these could be literally anywhere in the urban/suburban environment" structures and landscaping will remove that type of character, which currently exists.
Think of the stretch of Route 2 inbound just before Alewife. Objectively -- from a property value and safety standpoint -- the ho-hum, brand new condos and apartments that now sit where the old, abandoned Faces nightclub used to be represent an upgrade, but from an experiential standpoint, that spot has absolutely lost "character" (albeit somewhat sketchy) in favor of complete anonymity and utterly forgetful design.
I'm not advocating for abandoned buildings over much-needed housing or vibrant office- or lab space, but I think it's pretty clear what Ruari was getting at.