I'm going to post this in two threads, but here has been my experience with my instrument cluster. I'll tell you the results first, which is kind of a summary of all the previous advice.
I've had intermittent speedo/tach/gas going to 0. Disconnecting the 3 wire plug shows the same problem. The lots of wire plug has the power and all of the notification lights. I believe the 3 wires are the canbus connection. When you turn the car on it will attempt recheck the connectivity (I don't believe disconnecting the battery is required or additionally helpful). Power surges from the AC or HID headlights can cause it to reset and recheck the connectivity as well.
The fix is to check/improve all of the points along the canbus connection. My connectors were not loose. So, I decided to attempt to get a better connection within the 3 pin connector. I was able to take apart the 3 cable connector and bend the internal contact to intrude further into the pin. I'm not sure if this has fixed the problem, because it is intermittent, but I didn't make it worse.
I'll report back later if it doesn't work. I have some pictures of taking apart the connector, but I haven't copied them to my computer yet. I can share them if requested.
How I determined the above:
My cluster would stop working seemingly randomly. Sometimes it would fail when I turned it on, and sometimes it would be while driving. I successfully used turning on my AC to get it to start working again. That worked for a while, but wasn't perfect. (I never tried turning on my HID's to see if that could cause the reset as well.)
Taking off the instrument cluster's main difficulties involve making sure you find all 6 screws on the bottom shroud, and having confidence in pulling out the upper shroud. Once out, there are just a few more screws to get at, and it comes out easily enough.
I tried all 3 ways of connecting the connectors. Connecting just the 3 wire does nothing. Connecting just the lots of wires connector allows it to turn on and display the error lights, but does not show any speed/tach/gas. Connecting both works like normal.
If your display has gone from not updating to updating, the easiest way to get it to get the gas to update is to turn off and on the key. When it first starts, it reads the gas level, then it smooths the value from there. So, if you are showing 0, it will take a long time to smooth it up to the actual value.
The turning off/on the HID/AC will only 'fix' the problem if the connectivity has been restored. Because it is an intermittent problem, it may take some jostling to reconnect.
Also, as brokenboy said above, if your needles are not settling to 0, there is a way to reset the needles in the manual.
2005 Laser Blue Elise, base model (with 2 oil coolers), Bridgestone RE-01R 205/45/16+245/40/17, 4Tress harness bar, 6-Point Schroth harnesses, Cup Car Ohlins, Blackwatch Racing adjustable anti-sway bar, ekological HID kit, Sector 111 rear panel eliminator, 2bular 7" single tip exhaust, Sector111 DOWNLow seat, Sector111 tiny mirror, Braille battery, LidBone, multivex side mirrors, snorkel delete, infinity kappa 42.7 front speakers, acousti-stuff behind rear speakers. It adds up so quickly.