Driving short distances promotes acid and moisture buildup in the oil, and this acidity causes seals to perish quicker and sludge buildup. Drive about 60km with oil up to temp to remove moisture. Also, an engine that doesn't run much can also dry seals out causing many leaks, so I would want my oil to be in almost perfect condition for an engine that is not used much.
That is why I would say 5000km or 6 month intervals for oil changes. It might cost more but then you know you always have good lubrication, and little sludge. Also remember that oil cools your engine, so keep your oil fresh. This is the one place you can not afford to skimp.
Regards
Jacques