What are you looking for in 1st class ?
If it is a solo seat, you can get one usually. The seating in 1st is 2+1 as opposed to 2+2 in 2nd class. However the solo seats are taken quickly and if you are booking close to departure none could be free. Nevertheless the pair seats are wide enough, wider than 2nd class. There are also more legroom.
Service at seats from the dining car is hit and miss, you are supposed to be able to order from the ICE portal using the train Wifi but I never seen it work in practice. Although usually the attendant will pass asking for orders. Wifi is the same in 1st and 2nd class.
I tend to book 1st class if the journey is more than 2h30 minutes typically, and I know which train I will take, without need for flexibility. But if I need flexibility I take a 2nd class ticket as the price hike to a flexible 1st class ticket is high.