5w20's may be good for most cars, but VW's tend to like more robust oils. I'd stick with 5w40 or something similar with the correct VW rating. Keep in mind your same car in Deutschland prolly comes from the dealer with 15w40 in it, despite being in a cooler climate.
As for short trips, take your car out once a week and run it really good. I mean REALLY good, it needs, no, it BEGS to be red-lined and taken through the gears at a brisk pace and yearns for a nice brisk highway run.
I do lots of short trips during the week. Last night i changed the spark plugs in my mazda (new NGK Iridiums) cleaned the throttle intake and air cleaner, then took it out on the highway for some full throttle starts from 0 to 80 mph and mid-level punches from 40mph to 80 mph at full throttle. The new Iridiums and cleaned up throttle body really made the mazda 2.5 v6 come alive.
I hope i didnt thrash my havoline 5w30 too much
(of course always obey speed limits, safe driving, bla bla bla...)