hmmm...
1. 32 GBP for the original PS2 rgb ????!! This IS expensive... Are you sure, that it´s not a special one with a build in Videorecorder ??
2. I´ve used my "old" PSX rgb cable too and I must say, that there IS a diff. between the "normal" 3 Cinchcable and the rgb...
3. If you want to see the diff., just switch your TV from rgb to "normal" and you will see it ! Well, as I said before, the diff. is noticeable, but not THAT much... while "PAUSING" a game, look at the snow and the board to see how sharp the edge is now, than switch back to "normal" cable and you will see, that it looks greasy...
Nevertheless, it´s a better pic with rgb, not mindblowing, just better... and without spending much money !

Edit: Maybe you should try to adjust the sharpness on your TV a bit ?! I´ve done it with good success...
2nd Edit: Maybe you think of the texture by saying that it doesn´t look sharp ??? This is not a problem of the cable, but of the PS2... The first games has to cope with the 4MB Vram limitation... and that causes a "washed out", not so crisp texture... nowadays there are ways around this limitation !