what is more important ?

Hiya ,

Just wanted some views/opinions on what is the most important piece of equipment in the reproduction of sound/music.

I know and have heard that the dimensions of the room has the biggest impact but what about the speakers, amplification, and source... which one would give the biggest sonic differences(for better or worst) if replaced ?
If my current system needs upgrading which part of the chain should I focus on first to get the best 'bang for my bucks' ?

Cheers all

hiya Folks,

do interconnects and speaker cable make any significant difference?

The reason I am asking is because whenever I ask staff at Hifi shops they are always trying to flog me expensive cabling.

Cheers again
Cables make very minor differences, and that's what actual measurements reveal. 

This hobby gets most expensive and frustrating when legitimate analysis of what you're hearing isn't taking place, but rather, going to forums and pitching questions about what equipment will do what to achieve your goal, or just blindly buying gear with no grasp on what it does on a basic technical level. 

I recommend starting small and simple and learning for yourself. Nobody can actually explain to you what different distortion sounds like, and that's what distinguishes one system from another. 
Yes but they are close to last on the list.  
Want to guess what the most important piece of equipment is in a car? The nut behind the wheel.

Same here. If you know what you're doing you can build a budget system that sounds just wonderful. But if you don't, then no components under the sun will ever get you there.
Speakers. The difference between cheap speakers and good ones is huge. The difference between a cheap anything else and a good one not so much except maybe cartridge. The speakers will determine the sound of your system more than anything else. With good ones you will be able to appreciate upgrades in other components. 
Georgehifi, humidity does not effect the efficiency of ESLs unless you have adjustable bias and are forced to turn it down. Most of us adjust the bias to the highest point satisfactory for all conditions as bouncing your bias around screws up settings with other devices like subwoofers.