like any car they arent too bad if you leave them standard.
i think those are still affected by mitsi roof rust (usually requires a complete roof replacement) and as mentioned the drivetrains arent the best out there, and typical mitsi lifter click. I think the ECU's also shit themselves in them quite commonly too.
run it on a minimum 95, or 98 if you're feeling rich. the cars ECU should recognise its getting better fuel and adjust the timing to suit. there won't be much tuning that can be done on a factory ECU, but its always good to do a dynorun to check the A:F ratios are in order and there nothing alarming going on.
if you were really smart, and as there seems to be no backing off in gas prices, i would sell it and get a caldina GT nonturbo. the libero has 205hp factory and the caldina non turbo 191hp.
not a major difference in power, but way more practical and good on gas