You may have trouble getting through resume screens and picky HR drones, but fortunately this only seems to be an issue with large employers who are more concerned with filtering out resumes than looking for the perfect developer. Small employers and software shops simply tend to be more open to people with varying bakgrounds.
If you can demonstrate on your resume that you had a number of responsibilities, took leadership or ownership, have the ability to quickly pick up new domain knowledge then these are all things that shine through what you are working on specifically. Furthermore if the legacy technologies and poorly written software that you maintain are such that you can identify everything wrong with them and how newer technologies improve upon or help prevent these pitfalls then you are better than most.
I would want to work with such a person described above over a poor developer that does not grasp these concepts but has direct experience working in newer technologies.