i have the same model civic... and i had it converted to CNG abt a year back... this car runns perfectly perfect on CNG... i never had any problem with that... the acceleration is also gud... atleast better than what i expected... in one cylinder (55 litres) it runs approx 130 to 140 km in city... and this mileage fer a 1500cc car is gud... with a little compromise on performance... (ab petrol aur cng mein kuch toh farq ho ga na...)
and about changing ur car... its totally a seperate thing... if u think u shud change ur car u shud... CNG shud nt effect ur decission unless ur going fer some diesel car...