The problem with "consumer"/"home" routers is that they seem to go out of their way to make it hard to troubleshoot things, and the manufacturers seem to have no concept of the fact that "Oh just unplug it for a minute and plug it back in" is really NOT an acceptable solution to problems.
That said, there's really no physical reason why a WRT54G series router couldn't handle your average small office environment from a purely hardware standpoint -- your problems are likely tied up in the all-in-one software that ships on these devices.
Adding more routers (probably) won't help: Unless your routers can't physically manage coverage and you have signal dead zones adding more units will just add to the WiFi noise and slow things down.
Trying alternative firmware is also an option, but you won't get any support from your vendors if you do that, which is a consequence you'll need to weigh carefully (along with your budget).
My usual recommendation for someone in your situation is to get away from the all-in-one consumer hardware and invest in a properly separated infrastructure:
- Modem device (which may be incorporated in (2) below - like T1 WICs)
- Edge Router
- Firewall (sometimes incorporate into (2), but usually better separate)
- Ethernet switch(es) as needed
- Wireless Access Point(s) as needed
This costs a lot more than a cable modem and Linksys all-in-one unit (which often drives people to the alternative firmware route) but it gives you a much more flexible configuration, the ability to replace single components when they break, and most importantly vendor support if things don't work right.
Often you also have much better debugging capabilities: Pretty much every decent edge router, firewall, switch and WAP will have serial console capability, and you'll be able to plug in and look at error messages on the console (with the vendor) when things aren't working the way you expect.