The only time you should be 'replacing' your anything is if you have to - if it's burned (vehicles, abodes, IDs) or if it's battered (armor, weapons, gear). If you never had a problem with the Hyungk of Jyunk CanRay's talking about, then why replace it? Sure, get another one, but don't throw the thing out just because it's old.
In most shadowrun games, you also aren't going to be wasting most stuff (ID, weapons, vehicles) on a run. If you have to get something just for that run, you should look into how quickly and profitably you can resell it - talk to your mechanic or chop-shop contact, how much he'll give for the thing. Or, if you're paying attention and know you need a disposable vehicle or two, you ask chop-shop guy if there's anything he's looking for, swipe that, and basically get paid a bit extra to have your ops vehicle diced into anonymous parts.
Otherwise, Joker, depends on the area - and the target. Generally, you really WOULD want to show up in something bland; for one or three people, overall a Jackrabbit/Comet is the way to go. And if you're trying to remain inconspicuous, usually you'll want to go in two or three seperate vehicles....