What sonars are you guys using?
The test we did with our sonar was accurate at 18 feet but a little thing such as a chair backrest threw off our numbers enough that we are reluctant to using it.
We were using the LV-MaxSonar-EZ1
You can compensate for spikes and noise by using a moving average. This year we have one LV-MaxSonar-EZ1 and one MB1361 XL-MaxSonar-AEL1 (10 Meter). We really wanted to use one from here, but it violates all sorts of rules 
Our experience with sonar in 2011 was an unmitigated disaster (and that is putting it positively).
You have multiple robots and multiple points of sensing throughout the field. Robots are moving around. Game pieces can get in the way. It is not reliable.
We finally removed the sonar senors pointing outside the robot and tried to use it to sense the height of our elevator (a long distance). The robot vibrated, the elevator wobbled, sudden hits, etc. Even that was not a reliable use of the sensor.
If we try it again it would be only internal to the robot and near the shorter distance of the sensor, and well tested in gameplay situations.
What are you trying to do that can’t be done with a more reliable and repeatable sensor?
The Maxbotix sensors are awfully reliable and repeatable, in my experience.
Certainly, as with any ultrasonic, they are susceptible to noise and will only return the ‘nearest’ target - all of which is not a fault of the sensor - but don’t condemn the product if it works as advertised.