We provide migration services to many Teamcenter customers.
You have a few options, it depends a lot on how many files you have, and a lot of business questions.
The command line import (swimimport) and bulkimport are cery useful and are being blended together in the next release of SWIM. These work great if all aspects of you data are correct. However, as you discover issues, you will get into a loop that may be easy or almost impossoble to get out of - depends on your expectations and the data.
Keep in mind that you can create a SWIM.XML file suited for Import that permits or support different things than what you use for interactive use with new data. Than can help leverage existing attributes for example.
There are a million details here, let me know if you have some questions. Also, if you want to see a demo of how we see people can use SWIM with Teamcenter check out these videos. They may give you some ideas about how to use Solidworks and Teamcenter as well.