First off, you are talking in Mb/s and not MB/s correct?
The problems you are experiencing are not entirely unusual. The WGT624 uses an Atheros 500x chipset. I've seen many of these routers have problems with newer wireless NIC's. Sometimes upgrading NIC drivers or changing settings in the NIC can help, but not always. The odd thing is that the problem doesn't occur in all routers that use these older 500x chipsets so I suspect most of the problems are about poor firmware implementation.
I assume you've already checked to see if Netgear has newer firmware for your WGT624? Are you using WPA security? Does your version of the WGT624 support AES encrpytion? That would be WPA2 AES. If so, try it.
Are you experiencing the same poor bandwidth on LAN-LAN traffic? If LAN-LAN traffic is faster, but LAN-WAN is pitifully slow, you may only need to adjust your router MTU setting.
If all else fails, yes upgrading will help. I don't know much about the Buffalo model but Tim's preview looks interesting. That said Tim's limited testing doesn't always uncover problems (not Tim's fault). Its in real world, extended use testing, that people begin to see router limitations/bugs, etc...
I would recommend you try the Dlink DIR-655. If you experience problems check the user forums at
http://forums.dlink.com to see about newer firmware that may work better for you.
You can also consider upgrading to one of the mature 802.11g products. Some have been around for a while and have fairly reliable chipsets. I can't point you in the right direction per se but a friend of mine buys the Linksys WRT54G (new internal antenna version) and uses them in the field a lot with few problems.