I would get the problem fixed before doing any modification.
Performance wise...1.4 16v..75bhp? You could always add a manifold, full exhaust, forged internals. Or a remap for an extra 5 horses. Due to it being low displacement and a n/a engine, its really pointless. I no what you mean, i also have 1.4 and was eager to do it up, but i have friends who have spent thousands on a 1.4/1.6 and it will maybe pass a 2.0n/a, but anything with a turbo init and there smoked.
If your planning on keeping it a while, drop a new engine in it, or i read that i guy added the tsi system to his 1.4...mark v tho. Maybe worth a look into.