Both the Vios 1.5 and the City 1.5 have aftermarket options for them... there's an original TRD turbo 1.5 (just don't ask me how to get one), while the City/Jazz 1.5 has quite a number of tuning parts from Japanese companies.

But if we're comparing VVTi to iDSi, that's apples to oranges. VVTi, just like the 1.5 VTEC, maximizes power from the small engine, while iDSi is more focused on fuel efficiency.