Here are some specific ways the import wizard could be improved:
Fix the High-DPI issues (I think you're already working on that).
When an import wizard fails due to incorrectly detected data types, you have the information required from the error messages to recommend an alternative data type for columns
What I end up doing in the real world when I hit these is to open the .tim file that I saved during the import in Notepad ++.
Unfortunately, the XML that you write out as part of the import wizard is not formatted so it's an absolute mess to try to edit manually. Notepad++ makes up for this with it's "Pretty Print" add-in option:
The point of this is not to teach the community about editing .tim files with Notepad++ but rather to point out that when properly formatted the .xml produced by the .tim file format is actually very easy to edit and correct data type errors.
.tim file extension is not associated with Toad by default. Just seems strange that I can't double-click a .tim file and end up with it loading in Toad.
At the end of the wizard you ARE presented with the option to re-start the wizard, but it does just that -- restarts it ... seemingly without keeping any of the valuable information learned from the previous loop -- such as info about the data type failures. Why not restart it at the data types screen with those that failed highlighted somehow?
On the data type suggestion page, why not add a button to sample more rows? I for one wouldn't mind clicking a button to set rows to sample at something like 10000 rows to get better data type detection.