Thanks everyone for the fantastic and helpful responses!

I suppose I should my priorities in this order of importance for my commuting bike as a whole, where number 1 is the most important:

1) Safety
2) Reliability
3) Comfort
3) Speed
4) Style and aesthetics

I am contemplating actually changing the bike before spending time and money on new tyres. I am commuting on it daily now and seeing the flaws of the bike. Such as:

- Bike seat keeps rotating back if I hit a bump hard. Even though I am tightening it up good. Not sure how tight I can go without damaging the fixing?
- Gears are not changing smoothly, especially when I need a quick shift to pick up speed, etc. It sometimes does not go onto the low gear on the crank without playing around with the gears to get it to shift.
- Top gear on the flywheel slips

I am not sure by the time I spend the time and money changing the drive system, tyres and maybe a new seat. That I couldn't sell the bike, put a bit more on top and buy a more reliable and higher quality road/hybrid bike?

I am so eager to buy a road bike (like a little kid that wants a Ferrari!) however I am not sure a road bike would be the best solution to match my priorities listed above

At the moment I am really enjoying commuting on it, even in the wet and cold. This bike was always going to be a stepping stone to a better commuter, but that next step might come earlier then I initially thought.

Thanks again everyone!