I wouldn't do it for 2 reasons.
First, saying that you have experience as you've driven as SLK for a fortnight, and a couple of others for similar periods is laughable. What real experience does that give you of varied conditions, roads, driving hazards etc - none!
Secondly, unless you have far more money than sense, you will have that niggling 3k excess ruining the experience for you. You'll worry about everything, where it is parked, vandalism etc - things out with your control that could still end up you payin that excess. Or you need legal aid/personal injury aid etc etc.
Remember that whilst it is easy to say that if someone hits you then their insurance will pay, all insurance companies try to get out of paying and even on a clean cut case you could wait months to get approval to repair your car. You only have two options then - pay for it yourself and try to claim it back (good luck with that...) or you stump up your excess, get the repairs done and let the insurance company fight it ou for you ( also taking months, but you get your 3k back eventually)
Speaking from bitter experience here - always have your excess ready to pay immediately or you could be without your car for a while.
Also, I agree that a 335i is an insane first car and that the premiums excess are probably justified (not 'stupid' as the OP stated). I'm on my second RWD car (with low power admittedly) but it does take building some experience to know what you can get away with before it is going to bite you. I've never driven a 335i, however I dare say on a wet roundabout or bend it doesn't take much to lose it. I know what I can get away with now, but with low power I've been able to build that up.
Last edited by Rob318; 02-24-2013 at 04:43 PM.