i dont really know what would be the over hauling cost. Generally the smoke is light bluish when you need to have the engine over hauled. you will also be able to smell burnt oil if go go near silencer after driviing your car for a few km.
i have a spectra, Al-hamd-o-lillah it runs fine, no sound, good control. i have used it motorway, it has good control.
regarding engine swap i think that over hauling would be simpler option, since you will not need to make any alterations to the car itself. i have experimented with my Fiat (fitted a Toyota 4E-FE) and i think that i think that alteration if done properly improves your car, but if not done properly can actually ruin the ride.
besides if you are stilling willing to swap the engine, in my opinion Spectra's engine would not be the best choice although its working out well for me, but its heavy and quite big. i have driven a classic but i think you need to have a lighter engine and 4E-FE should be put in the list of engines t be considered. i have had good experience with this one. it gives around 17 km per lit on the motorway (driving at around 100 kmh without AC).