Upgrade the network, or leave it as-is?

Hey all,

I've got a general question about a wireless network being used to share internet throughout a 100 year old 4 story apartment building (each floor has 6 units, the building has a square footprint), and if the setup should / could be improved.

The current arrangement (very low-cost, I know):

We have three WRT54GS v2.0's being used in 802.11g only mode with their stock antennas and DD-WRT. The one operating as a router is on the first floor, connected to a cable modem. One antenna is horizontal for an up-down signal plane, and the other is vertical for an "across the floor" signal plane.

One floor down in the basement, we have another unit set up in Repeater/Bridge mode directly beneath the upper one with one antenna placed horizontally with a reflector directing the signals to and from the 1st floor and one antenna placed vertically to broadcast across the basement.

Two floors up on the 3rd floor, we have the third unit directly above the 1st floor one, with a similar Repeater/Bridge setup and antenna arrangement (one horizontal with a reflector directed down and one vertical).

The Problems:

In general we have problems with signals penetrating the old hearty construction of the building. Some tenants at the edges of the floors either cannot connect to the network or have intermittent connections with very slow speeds (I understand that those connecting to the bridges will inherently have 1/2 of the max possible bandwidth.)

The Question:

Our building owner is wondering if there is any way to improve our network, and me being no specialist outside of being able to install and configure DD-WRT, I thought I'd ask you ladies n' fellas if you had any ideas to help the situation. Right now I have two possibilities:

1. Purchase upgraded antennas for the existing routers/bridges.
2. Purchase new routers/bridges using the 802.11n standard (Likely Linksys Exxxx series router with two RE1000 plug-in "range extenders" as I won't be there to configure anything that isn't nearly plug-and-play soon.)

Will improved antennas help signals penetrate the building any better? Does 802.11n perform any better in getting through hearty walls than 802.11g does? OR is the setup about as good as one will get for such an unfavorable building configuration?

Thanks in advance for any and all feedback you can offer!

Given all the views and no comments, I can only assume I have a flawless network! . . . or that it is such a hopeless network that no-one will dare touch it with a 10 foot pole!