Walmart's often get passed by town councils or whatever because they want the property tax revenue from the development. The thing is though you can't count on Walmart to stick around. I've been trying to recall the name of the city here in CA but I can't, but anyway they got approval for a store even though the residents of this town were largely opposed because the board wanted the tax revenue. But the city gave Walmart all kinds of tax consessions to build there (which is b.s. in the first place, it's just arm-twisting on behalf of Walmart). Mere months before the tax consessions were going to expire Walmart moved like 2 miles down the road into the borders of a different town, they were only in the original site for 2 or 3 years or something like that.
Oh wait, just did some better googling- it's Cathedral city. There's something about it in here:
http://www.goodjobsfirst.org/pdf/wmtstudy.pdf
Anyway, they do this all the time, apparently. Get in because they dangle tax revenue in front of city officials, meanwhile getting huge tax concessions for moving in for a number of years, and then when the concessions run out they move the store. So just from a fiscal standpoint, you can't trust Walmart.
And from a low-prices/jobs standpoint, the other carrots they dangle- more jobs and more stuff cuz it's cheaper- that's all b.s. too. Walmarts that are located in such a way as to dominate an area exert a downward pressure on wages which pretty much cancels out any "savings" they might bring to the consumer.
There's better stuff on this but I don't have the time right now:
http://www.slate.com/id/2113954/
It's all b.s. and it's not hard to find the data you need to illustrate it.
One thing though- I doubt your board members will appreciate emails from people who live nowhere near your city. I don't think it's a good idea for you to encourage random people on the internet to contact your board members. A city official's job is to serve the people of the city, I think emails from elsewhere would have a negative impact.