G very rarely, if ever reaches 54Mb/s - if the OP has a decent Internet connection such as ADSL2+ or VM 50 meg then an upgrade may be useful. I did some quick tests with iperf over G just out of interest and through walls I was getting something like 10Mb/s
IIRC, even though link speed was 54Mb/s according to Windows. Also N is rarely faster than Fast Ethernet for the same reason.
IMO wireless is good for mobility (laptops that get moved a lot for example) or as a last resort where cable simply can't be installed for whatever reason but if it's possible to install it wired is better every time.