A car using rear torsion bar will never handle well, even with modifications. All the cars listed most are using torsion bar.

Like said, best bang for buck would be the Inspira, for 2nd hand just go for Altezza. Japanese BMW killer.

Or if you are feeling racy, get the DC5R. Or the older brother, DC2R. Double wishbone suspension, the best money can buy.

Yes, but do look at the chassis design as well. To compare with Vios, Forte, torsion bars are used to save cost, get more room for the trunk and rear passenger as well. Different design for different purpose, but then again, how many sports cars are using torsion bar?