I have never heard anyone mention any capabilities that Inkscape has and Illustrator does not. Illustrator is the tool of choice for many professional cartographers, though, so I think you're safe sticking with it. Look up posts by HandsomeRob if you'd like to see some awe-inspiring Illustrator work. He's a pro cartographer by day and has been making a very detailed fantasy atlas in his free time. Although I haven't seen him post in quite a while, now that I think about it.

One place where Inkscape might have a slight advantage is in compatibility because it uses SVG as its native format.