Import is just another proces that stuffs data into the database. Having your database tuned improperly will always be the bottleneck in an import.

That being said, there are a couple of ways you can help imp to do his job:
1. Use direct=y in export. A larger db_block_buffers will not help you if you used direct=y because the insert operation bypasses the cache and drops the data into the files directly.
2. Don't pre-create you indexes, let imp create them when he wants to. Pre-creating you indexes will create an unnecessary burden on your index disks.
3. use the commit=y flag along with an adequate buffer= flag. The default buffer size is inadequate. We have seen performance increase by up to 4x when commit=y and buffer=4000000.
4. Make sure your data files are seperated from your TEMP and RBS.