Wotcha and welcome - as above hi flow panel filter, cat back exhaust (when your existing fails) for a little more rumble is as far as engine needs to go, look at chassis mods, brakes, ARB, suspension could be a bit firmer - think about power to weight ratio, where can you drop some weight.
But if all you do is spend money on giving it a full service, replace all the fluids, spark plugs, dependant on mileage the belts and pulleys etc that is ok
With my RX I didnt think the alloys filled the space enough so I bought some spacers, haven't bothered with any power orientated mods