I don't have specific experience with the Speedbooster, but if you're doing a lot of file sharing between Mac and PC, then it might be worth it. If the wireless connection is simply to get to your internet service, then you may not notice a difference.
Generally speaking, wireless speed drops off relative to distance from the wireless router. Speedbooster may give you better speeds further from the base than their standard product. I haven't noticed any real-world problems using the regular version with my broadband connection.
The print server thing may be nice, though, since I don't know if the print sharing works Mac to PC (edit: OS X built-in sharing, that is, not the SMC print server). Linksys makes a wireless print server that you attach directly to the printer, but then you have two devices. Of course, if your printer isn't naturally located near your router, it may work out better.