Although this has already been stated, I hope this helps - I agree that you will face a glass ceiling when it comes to competitive residencies. It's not a matter of discrimination - it's just that these programs have so many excellent candidates to choose from based on those candidates' school names and opportunities (research and leadership opportunities). However, the question I would wager to you is this: Do you feel that you have a desire to pursue these top flight residencies over the potential cost of a lost year of salary?
If the desire to be "the best" is of utmost importance to you and that rubbing shoulders with the greats is necessary, go for it. If you're deadset on a specialty and need access to those fellowship/competitive residency opportunities, it may be worth your time. Does the need to do some kind of specialty research pique your interest? Etc etc. When you wager your sure-fire position, what do you hope to achieve by doing so?
However, if you feel like you're going to lack in education or boards scores as a result of going to a DO school, I'd argue that you're putting too much weight on the school and not enough weight on your own work ethic. The hidden cost of medical school is in the debt - interest never sleeps. It does, however, compound. Furthermore, you're not losing a 1 year of your youth. You're losing out on one year of attending level pay before retirement. One more year of putting your life on hold while you try to enhance your application when there's an army of candidates who are looking to do the same thing. Ultimately, you have to weigh the cost of mounting interest and a hold on your life over the possibility of achieving your absolute potential.
Only you know your application and life goals. Just my $0.02. Cheers!