Jan,
He wants your 28/2.8 Elmarit Plus $1200? Boy, that's a terrific deal FOR HIM!
Also, which version of the 28? There were several and the earliest I believe, is the more valuable.
KEH has several 28's right now in the $1500 range and no pre aspheric 35 1.4's The 28 is usually sold without finder which would add about another ~$200
Prices have increased significantly for most M-mount lenses since the introduction of the M9. This pre-ASPH 35mm Summilux has developed a bit of a following. Frankly, if I were in your shoes, I'd consider the 35mm f/1.2 Nokton and keep the 28mm Elmarit. I have a 35mm Summicron as my general 35mm and I use the Nokton when I need the extra speed.
Giving legendary Elmarit for Summilux , not a good idea. www.imx.nl , look for Summilux versus Elmarit tests. If you are not blind , you will understand what I am talking. Elmarit is a Leica lens , Summilux is a camera lens.
Dont handle the hot pan Nokton , it has never closed to Leica quality. Stick to your lens and buy an tele elmarit with your money.