I would like to know if a Gas conversion on a small hatch is worth it?

not worth it as already said the car is old (no offence!!) but gas is harder on an engine, higher temps etc. gas doesn't have the same amount of energy in it, so you need more of it (that doesn't make sense really but you follow my drift?), on a small car the gas will steal the engine power but you will also need a decent sized tank so it is partly useful, this has a lot of weight in it also which will weigh the car down creating more drag, making the engine work harder, using more fuel... its a big circle of things..