I reached silver for the first time last year (flying only Y inside Europe plus domestic connections - company travel policy) and will comfortably retain it this year (similar pattern with a Y+ to DXB and a Y to JFK). I am also gold on KL (just dropped down from Platinum) which is broadly similar to BA silver.

My situation is that:
* I am free to choose my own carrier & routing for my company trips as long as they are in cheap Y
* The benefit of seat selection as a BA silver is worth a lot to me for family trips
* I have 220 tier points in the bag for my next tier points year starting in July
* I am sat on around 250,00 avios
* Even after the changes, BA will give me slightly more miles than KL for my regular trips

But...
* The removal of the free regional connection on avios redemptions makes BA far less attractive than before
* I do not do enough flying (combined BA & KL) to hit gold on BA
* Platinum on KL is not worth that much more than their gold (and milage earning on KL in Y is terrible)
* KL is often more convenient as it serves an airport 10 minutes from home while NCL is a 45 minute drive away
* Coming back to the UK, transferring at AMS is a better experience than LHR

My conclusion is that I will pick the most convenient flights for me regardless of if it is KL or BA although I will ensure that before the end of the year I will definitely get the 30 segments on KL to retain my gold status. Once I am sure of getting that I will review my BA earnings and see if silver is a realistic possibility.

I realise that I am not among BA's top tier of profitable customers so I guess I just have to weigh up who values my 120 annual segments the most.