would bet those on dialup ... are not going to be big online shoppers
That would be a foolish bet, IMHO.
I often think that people who claim that dialup users spend less have created that very situation because their sites are just too frustrating to use on a slower connection.
People on slow connections WILL spend money online, as long as the process isn't made intolerable by needlessly sluggish site behaviour.
People in rural areas have fewer local shopping choices but they have just as many needs and wants as anyone else. Online shopping is an attractive option when the nearest mall is hours away, and if you provide a workable shopping experience for dialup users, you'll have a good chance to gain them as loyal repeat customers.
One easy place to make speed improvements: tweak your templates to reduce redundant white space from your source code!