No offence to the mechanic, but his statements do not go along with what you have and what you want. Indeed I agree with him that you can't change a mule into a racing horse. Then why suggest a bolt-on kit? It totally conflicts with his own statement.
The fact is, you own a Charade and might not be able to afford a "racing breed". The fact is, you want more power but do not wish to spend loads of money. Which is why I suggested repairing and modding your current engine.
And in defence of our little Charades, one thing most people do not realise is that they have 2 characteristics in their favor: 1. high power-to-weight ratio and 2. very good low rpm torque. Slight modifications increase both factors and allows you to beat many more larger cc cars off the line. On my old CB23 the only mods I did to it was an exposed air-filter and a DIY port & polish. Just these 2 mods allowed me to beat almost any 1.3cc car and match most 1.5cc ones.