I just read my earlier post and I'm sorry for the slightly confusing language, but I was multitasking.
My point was that after a 500GB HDD, moving 'into' a 160GB SSD is a large compromise in terms of size. In a way that's fine, you can use your HDD as an external drive with a USB enclosure and keep the essential files on the SSD. But overall, where you will see the benefit is the boot-time and when launching applications. Your browsing, your media experience, the actual usage of most application will hardly change. In fact, you'll have to part from most media files, so it's going to be worse. It is fair to say that many of the SSD's benefits are illusionary, but others might argue with this point.
There is another issue. Your MBPs' value is around £700, maybe more? If you considered getting a new one, you will want a new one next year. The almost £250 that you spend on an SSD will be mostly wasted on this computer, nobody will pay the premium for it on the second-hand market. My advice is to use the computer as it is now, don't spend a penny on it and just enjoy your MBP. Next year, you can spend three or four hundred pounds on a newer one with much better overall performance.