Assalamulaikum Brother. As per your query, the simplest answer to you would be this :
If Upgrading to a 1.8 Varient, "Yes" the upgrade would be feasible as you get a smoother CVTi transmission and possibly better mileage and braking car due to bigger brake calipers and better (so called ABS) and you get a reliable car (Stability is questionable at high speeds due the the higher rear clearance and hunchback suspension if driven to the limits in all variants).
If upgrading to a 1.6 Varient from a non Altis varient (old 1.6 GLI or 1.6 Altis Non SR) "No", as you get the same car with a different heavier body with nearly the same goodies and nothing new. Even the mileage is lesser. The brake calipers are larger but the braking is not that different than the previous model. I would not suggest this upgrade unless ofcourse you change your cars with the shape changes or years or mileage, etc. Jazakallah.