I've been Silver several years (but not in a row, though). It's really nothing to write home about. The 15% extra points are probably the best, if you fly a lot of SK metal. The business check-in (i think this previously was only at Arlanda?) is a nice perk, but it's usually faster to do self checkin anyway. I have never needed the 10 extra kgs allowance, either.
If being *S my bet is to go for LH. Then you will have access to their C-lounges which are quite OK. Also, in the event of having a "good year" you will rather easy reach SEN status for at least two years (depending on when during the year you qualify) with many more benefits that are far better than SK's Gold benefits!
Best SEN benefits IMO are:
- 50% award for spouse
- e-vouchers