Upgrading WiFi Antenna Gain?

I added a pair of Linksys 7db antennas to an access point inside my one-level house but I don't see any increase in signal level at my router. I've also tried it by replacing the antennas on my router instead with no increase seen at the other end. I'm using the signal level viewer built into the DD-WRT firmware to check the signal. Eventually I'd like to increase TX and RX range (omnidirectionaly) at another facility without having to crank up the transmit power on both ends - thus the "improved" antennas. Did I just waste my money on them?