Hi and welcome to the forum!
I owned an E86 Roadster for 4 years and switched to an E89 7 years ago.
I'm 6'1 and built like a rugby player. I found the E86 to be quite cramped and long drives (4hrs+) would exacerbate my chronic back pain, and also give me knee pain too. I find the E89 cabin to be much roomier and more comfortable. More leg-room, bigger more comfy/adjustable seats, and a softer suspension. The E89 is still low to the ground, there's no way around that, but its not as low as my E86 was, and the back and knee pain I used to get driving the E86 just doesn't happen to me anymore.
I used to leave my car outside year-round in the Scottish weather so can confirm that leaks shouldn't be something to worry about, but would recommend checking your weather seals over and giving them a bit of Gummi Pflege every now and then to keep them fresh.