I fitted some Fli 5 13cm component speakers into the front and some 6x9 Fli speakers in the back.
In the front the main speakers were replaced easily with a couple of quid gtv converter plates from ebay. To replace the tweeter, I had to take the door card out and carefully drill a slightly larger hole with a holesaw and sand a bit more for a nice fit. As suggested, if you don't want the hassle of cards off, disconnect the original tweeters and don't buy component fronts.
The rears just dropped straight in. The original cloth grills fit over the top so it looks pretty stock apart from the tweeters which aren't too in your face and you could perhaps spray the outer ring black.
Overall it was a reasonably budget installation, the sound was greatly improved. Would like a bit more bass but that would require a sub, plus i would suggest the gtv would be a bit rattly with any more bass
Whatever you do will improve, the stock speakers are terrible!