can't afford to get stuck in traffic as the aircond doesn't cool when the car isn't moving... 

Mind sharing some pics of your ride?
Haven't seen a UK Spec kelisa before....except for the one JC destroyed in TG... 
Seriously the compressor? Previously was said to be the fan not cooling the engine bay enough?

My 4th gear 3000rpm =90km/h
5th gear 3000rpm =110km/h
I too have the weak compressor/hot air when hot weather issue
But two weeks ago just install tinted (first time after 10 years). In my opinion it helps =)
Last year I change my timing belt at my usual mechanic for RM250.

I'm not sure about inflation rate though..
If you can live with spending RM340, I will suggest go for it.
At that time the labour fee was about 50, when he fix a gasket leak for me together. So I can't tell exactly how much is it.

Dual airbags + abs maybe? 

You mean power Windows?
Mine is GXI (manual), front 2 has power window, while back 2 is manual operate.

Barring any major issue or unforeseen circumstances, I will still be driving my 'little white' for at least 5 more years =)

Timing belt only $2++. Usually change together with fan belt etc.

Sounds like belt to me. Easy way to tell is to drip water on each of the ancillary belts (on Kelisa there is AC, steering and alternator belts). If the noise changes that means that belt is faulty. AC belt is easiest to access (front of car), steering is on top, and alternator is hidden where even God can't see.
It shouldn't be timing belt. Timing belt has teeth, if gone can't even start the car. Might as well replace the outside 3 first.