Ignition system

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No car runs flawlessly forever. So before you begin blaming VW gremlins, start by examining and verifying all the traditional trouble spots you would suspect in any car. Start with the ignition system:

Spark Plugs
Your spark plugs should be of the correct type for your car. VW recommends Bosch WR7DS (S for Silver electrode) for the Digifant engines. There are plenty of arguments about silver and platinum electrodes. Call me a heretic, but I have found copper-electrode plugs (Bosch WR7DC) work just fine, give good life and are much cheaper.
Whatever plugs you choose, make sure they are gapped to 0.7 mm (~0.25 in.). Put a drop or two of engine oil on the threads (not on the electrodes!) before you install them and don't over-tighten them. Check your plugs a couple of time a year for gap and signs of wear or oil fouling. Like all modern engines, spark plugs in a healthy engine should have a brownish-tan appearance.

Plug Wires
Worn out plug wires can reduce or interrupt spark delivery to the spark plugs. Insulation softened by temperature extremes, oil and grease, and time can allow arcing which causes misfiring.
If you suspect your plug wires are not up to the job, wait until after dark. Start the engine and using a common household pump bottle, lightly spray a mist of water over the plug wires. You may notice erratic engine operation right away, accompanied by sparks jumping from wire to wire or from wire to engine metal as the water spray conducts current away from its proper path. The solution here will be obvious.
Replace plug wires when they begin to look really grimy to eliminate this potential trouble spot.

Distributor Cap and Rotor
Over time, the interior of a distributor cap will build up deposits of carbon called "tracks". Carbon is an electrical conductor and will interfere with the orderly distribution of current to the spark plugs. Remove the cap and rotor and look inside. Any black, grimy substance in there is carbon tracking. In addition, the copper contacts inside the distributor cap should not appear burned or scorched. If the cap is relatively new, clean up the contacts with some fine sandpaper, then wash out the carbon tracks with hot soapy water, dry and re-use the cap.
Look at the rotor too. Burnt or scorched copper rotor contacts can also be cleaned with fine sandpaper, but if the cap and rotor appear to be in generally bad shape, or if you've done the hot water and sandpaper routine before, it's time to replace them.
While you're checking out the distributor, have a look at the Hall Sender plug on the front of the distributor. The insulation should be intact. Remove the boot and give the plug contacts a shot of contact cleaner.