There are a few things that you can do to this engine without actually destroying it (but you might run into a few problems here and there.
1. BOT - the engine is a standard high compression engine so if you wanna BOT it, make sure you don't boost more than 0.4/0.5 bar of pressure or else you will kill the engine in the long run. Cost of getting all the neccessary parts, fixing it in and all will cost roughly in the margin of 3-4k.
2. 4 throttle or dual intake manifold - I myself am pretty interested in this mod but finding a suitable 4 throttle kit and modifying it will take patience and money. I have seen dome dual intake manifolds (basically having 2 throttle bodies at each end) that will boost your intake volumn to push more power. Make sure you have an upgraded fuel pump and injectors + some sort of air/fuel controller to give sufficient fueling and management. Improving the intake and fueling for this engine is the most basic of basics (actually for any engine) to produce more power.
3. Port and polish the intakes, exhausts ...and maybe if you are willing, rojak the engine with some parts from the bigger brother 4g93 or aftermarket products (piston heads, cams, crankshaft..bla bla....don't ask me what to change im unsure about this but i know some ppl have done it with 4g93 parts)
4. The 4g92 sohc bottom block has only slight differences from its dohc counterpart. You could throw away your sohc top block, buy a mirage 4g92 dohc block with mivec + all wirings, ecu and manifolds. This way you get to use your old botom block, rojaked with a dohc mivec top block, gaining variable valve timing. Your power gains wont be hell alot because you old block runs on a slight different compression compared to the dohc version (dunno I was told that)
5. You could slap on some Abang technology that claims to 'save fuel' and 'add power' and be happy about it. (I don't recommend this at all...because i think all that stuff is bullshit)