Hi I am going to be in San Miguel de Allende for a week beginning April 26th and had thought of "winging it" for a few days before Mexico City on May 8th. I don't know whether Cinco de Mayo is a holiday when people travel. Should I make reservations somewhere in the area? If so, suggestions?

5 de Mayo is not such a big deal in Mexico. Actually is just kind of a partial holiday because only schools and goverment offices get the day off.
You should worry more about May 1st (Labor Day) a recent change has ocurred. Now instead of taking the actual day (May 1st) , the holiday has been moved to the closest monday making it a long weekend. Obviously more people takes the opportunity of traveling during those days.
Make sure you have reservations during the weekend of April 28th to the 30th.

Saludos

Make reservations for 5 de mayo. I had to sleep in my car that weekend in 2004 because there were no vacancies ANYWHERE. It's always better to be safe than sorry.
On your way to San Miguel de Allende checkout "HOME" www.QueretaroBandB.com
It's comfortable and only 350pesos with breakfast.

Agree with Isela, 5 de Mayo is a near non-event here.
M (SMdA, Gto.)

I have always been told Cinco de Mayo was more celebrated in the U.S., than in Mexico.

although 5 de mayo is a non-event in Mexico, San Miguel de Allende will be full of AMERICANS that think that something great happens during 5 de Mayo. Trust me, 5 de mayo = non-event in Mexico. So - make a reservation

Enrique, just went on line and lots of res available here.
Saludos.
M

Enrique,
We, like so many others, we shall be away for most of hot May.
Have house guests and sitters and many dogs.
Lots of places are closed.
Perhaps you should live here full time for 4 or 5 years, lol.
M