Actually, there are two parking lots for the Boardwalk - one for the resort guests and one for "overflow" which is where anyone just visiting the Boardwalk for the fun should park. The overflow lot is across the street and a much further walk but it is there for folks who want to visit Jellyrolls, the Atlantic Dance Hall, eat at Big River Grill, or go to the ESPN Club to watch football all day on a Sunday. If Disney limited people parking for three hours to do any of those things, they would lose a lot of business for those venues.
To the OP - to get a feel for the Boardwalk, you can always exit Epcot from the International Gateway and then walk over there during the day. It's pretty dead then but you can see the layout. In the evenings, everything will be open.