Thank you to everyone who took the time to share experiences with relocating your farmers' markets. Below are the responses. I should add that the idea to pose this question to the list came up because Paul and Sandy Arnold told me that moving to a location with more convenient parking was excellent for sales at their market. It looks like others had similar experiences.

response  1) Our winter market has had four different locations.  Finding a space that is affordable, large enough and with convenient adequate parking seems to be the key, but difficult to come by.  
The Bennington Farmersí Market moves indoors from Nov to April, a distance of one block south and three blocks east of the summers outdoor market.  Parking for the winter market is less convenient and the space holds less vendors.  We also had Tuesday summer market that has been in four different locations, trying to make it viable- none work, the worst was downtown on blacktop.
A couple of times the market joined downtown events, Mayfest and Fallapoluzza, somewhat a disaster for vendors, despite lots of information before hand to customers, signs, word of mouth etc.
If the new location has better parking, ease parking, less congestion - any thing that makes it easier for customers to access the market and for the vendors to setup, then the move may go move smoothly.  We have found that there will always be customers that will be confused about the change (there are still folks in the area that do not know there is a farmersí market in Bennington) and vendors who just do not like change.
The move will need to be sold as a better space then what is being used now.

response 2) Many years ago we relocated the Richmond Farmers market and sales quadrupled or more. The new location is more visible, in the center of town, and has better parking- all key elements.

response 3) If the new location has great parking, good access, ample room for vendor displays and new vendors I would say the sky is the limit and the rest comes down to good marketing and management. 

response 4)  I led a move for the Portland, ME winter market and it made a huge difference for vendors on our normal season established peak sales weeks, and not so much a difference in our slow weeks.  The factors that I used to find a new market location included (in order of priority): 
1. Parking: Count the spaces (private lot, plus on-street, many lots in area so could run a shuttle if need arises with future growth, and bus line stop outside is a plus).  Estimated 2 people per car, 30 min (to 1 hr) per car stay.  Do the math to figure your desired customer count. 1000 customers in a market day /2 people per car = 500/4 market hours = 125 easy parking spaces for an hour (how long is average visit? 30 min, so half those 125 spots = 63 spots, but it might be tight timing to hit 1000 count with only 63 spots). Also include subtracting parking for the vendors.
2. Square Footage + Excellent Light (natural or electric): Nothing beats a large welcoming open space with great light during winter in the north country.
3. Schedule: making sure the organization or building owner has all dates available and is committed to a long term returning winter relationship.

Working with the City of Portland's tourist info bureau for booking business events /chamber of commerce was very helpful in aiding me examining choices in our rental price range, as Portland has been on the up and up and so are rents (based more for weddings think $4+k per day).  Despite working with the tourist info bureau, I ended up finding the location on a whim by calling all the schools with gyms or cafeterias within 15 min of downtown.  I based the location search on school and college cafetoriums (cafeteria-auditorium) or gymnasiums after researching SeaCoast Eat Local Winter Market's rental relationships with both a large nursery triple or quad bay greenhouse, and a Exeter High School in NH.  I also looked at the Armory system, but they didn't have the right schedule. 

The public schools with the most welcoming spots were booked out for basketball in winter.  We are in a girls' private school gym (their bball games are on Sundays) and cafeteria. Total sf is 9,700. Our current rental agreement included fees to cover the school snow plowing on market days (normally they do not plow on Saturday early mornings), a one-time fee for floor tarps to protect their historic wooden gym floor, 125 spot parking lot, and the rent fits our farmers' budget comfortably.  To get your ballpark desired square footage, it helps to have a basic idea of how much room and table space folks want, and then add paths and aisles.  We currently have enormous aisles (I think they are 10-12'), but the customers love the snow free space in winter, and the market is full with room to move freely and no bumping and packing.  As a mom of twins I can hold both girls' hands and not feel awkward when we stop to play in the aisle. 

Overall, I would say having one large open space to view all vendors from with incredible private parking does come with a school or college -- and those are things customers notice both subconsciously and consciously when they don't work, and make the customer experience fun when they work right. (No weird dark hallways and dividing rooms spitting up vendors, no awkward moments with strangers and their bags passing in 4' aisles).  Also, schools have a ready-made consumer base (of cooking families), dedicated and loyal local folks, and sometimes schools have a mission requirement to serve the community: a win win for the farmers' market!  

Elizabeth Wood
New Leaf CSA Farm