"they are auto trans so fitting cng kits will have an adverse effect as well"
it has no adverse effect.....the car will run fine on CNG. Depends who fits it, and whether u opt for complete EFI kit or not!!!!
If u r very very conscious about resale, dont buy it(Pakistani brothers start buying one thing like mad, and then next moment they stop for some stupid reason.) Else its definitely the best option in small hatch back.
good luck