No doubt changing from runflats to regular tires makes a huge difference with 20s...better handling, quicker transitions, less harshness. I did this on my previous M and it was very noticeable. I haven't done it on my current 50i, but only because I promised my wife I wouldn't.
By the way, modern high-quality tires have stiff enough sidewalls and sturdy build construction that blowouts are rare, and flats can be reinflated with a pump that buys you time to get to a tire shop for a patch. I've had a number of flats but never a blowout...you aren't going to see a Michelin tire delaminate stranding you on the side of the freeway.
2011 Nissan GTR Red/black - HP Logic tune/midpipe
2012 BMW X5 50i M-sport Dinan stage 1 Space gray/black
2011 BMW M3 convertible Jerez black/beige
Gone but not forgotten: '12 X5M, '07 AM SuperVantage, '05 Boxster S, '01 BMW M3,...