Insurance on a 3 series will be high. My dad is 47 has a clean licence and one crash and he just paid over £550 and he's been driving for 30 years (cheapest price with admiral after haggling). Remember its not just about power, it's about insurance groups. I've tried loads of different cars that had different power outputs but different makes, and you would be surprised what it would cost for a car with a fancy
badge with the same power as something thats considered a 'normal' make.
Can understand why you get bored though, i'm the same tbh. I'll be on my 3rd car and only been driving for 2 years!