(That was a bit confusing when I landed on the first page of this old thread.)

You can test your wheel sensor: while off the bike, spin the wheel with the sensor. if your GPS (Garmin?) shows random very slow speeds, it's using the GPS signal, which randomly drifts around your location if you are stopped. The wheel sensor will show the fast wheel rotation speeds.

I like having a wheel sensor on my Garmin. It's more accurate on slow, steep climbs, and handles starting and stopping a bit better. It's not critical, though.

I'm not sure why your climbing recording showed those odd dips. Try uploading the recording to ridewithgps.com, and see how it looks there. They have different smoothing methods.