There is several way to increase your wireless range (the one you already noticed) i guess all is pending your budget.
If you plan to change your router antenna for high gain one, then you could also have a look for how to create passive antennas as wall passthrough(ie: http://www.facebook.com/media/set/?set=a.178838405493117.36309.100001008769407 ), just because your customers will not change the wireless antenna of their laptop.
If you plan to get a second router, then it will be nice if it support repeater kind of settings (this will save you from drilling walls to place a long ethernet wire). If you want to save money then you could go to some opensource project like DD-WRT, OpenWRT, Tomato which turn some home use routers into professional one for free.
I am currently using a Belkin Play N600 Router at my motel. All the rooms are on the first floor but rooms that are farther away can only get 1-2 bars. The farthest room is around 40-50 yards away from the router. Play N600 is a router for a home so the range is really not that great. I have been researching some options and found out that there are basically three options1. Get a second router2. Get an antenna3. Get a new router with better rangeI believe the router I am using cost around 50-60 dollars and I know that a good router would cost around twice as much. I am not familiar with how wireless network range can be boosted, so any help would be appreciated!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic