Lovely car, configuration and colour
vivalaReagan 
Personally while I love the power of a black exterior for looks, I'm also a fan of lighter colour exteriors, they don't look as dirty as quickly, they don't heat up as quickly in warmer temperatures and some colours look just as elegant (your silver being one).
The black interior goes very well with that colour and I'd have chosen the same in your place. Agree completely with your assessment of the S v 7 comparison. I also tried out the S class and although the deals were far better financially here in the UK to go Merc, it felt 'dead' when driving it and indeed did have an 'older' person feel to it to me. While loaded S's can match the 7, base level ones are no match in my view (or when you put some options on it, comparing prices across.)
A weekend away trying both left me completely convinced the 7 was the better car to own and drive. I still love the way the S looks on the outside (not all models but some newer ones) but the drive killed it for me.
Those wheels look great, thinking of getting a larger set of rims for Summer use and been debating between 20 and 22" until now but maybe a good compromise would be 21" like you have here. Do you have the MSport version (not sure whether you get the same packages there as here in the UK)? Not sure what the Autobahn package is...
Anyway, my question is how do you find the 21" wheels? Do you normally drive in Sport mode or Comfort and do you find it 'harsh' with that combo (mode and larger wheels?) Some love the harsh or firm feeling, I'm more of a comfort fan so tending towards 20" to help slightly while getting nicer, larger rims still...
The 18"s I'm currently on are brilliant for ride quality and one barely notices any bumps in the car which is brilliant but the looks suffer...
Welcome back to BMW and to this forum, great to have you join us, do post more of your car and experiences!