Sorry to hear that you are having problems - I love my 1630 and so far she has been running strong. If it starts to have problems I would most likely try to get it repaired or try to find one to replace it. She sews so smoothly and does everything that I need.
The question of buying new or used will be dependent on your financial circumstances and sewing needs - you will have to weigh out the pros and cons to make your decision.
If I had to replace the 1630 I would most likely look at used because of budget and also because I feel that the older machines are more reliable, have metal parts and are built to perform for many years.
The new Berninas are extremely expensive and are way out of my price range so they wouldn't be an option for me.