wow, if your mileage is really that low then that really shows up how a car is way overkill to do the same job. You may be underestimating tho - I attached my computer to my mundo last week, and I've been surprised to find how far i was travelling - trips I thought were about 6km turned out to be nearly 10 etc. I think the ease of the bike dupes us into thinking it isnt that far. There's an important lesson there for many people who drive shortish trips because they think its too far to cycle.
On a related note, I did a 40km round trip out into the country on my mundo last week, just to see what would happen. Took nearly 3 hours (not counting a nap on the beach at the furthest point) cycling at a leisurely pace - proving (to me at least) that the mundo is fine for longer distances so long as you are enjoying the scenery and not trying to race.
keep pedalling!