Is it really worth spending a lot of money on a heavy bike? You will get far better value for money buying a new bike, which is lighter and better spec'd. All you will end up with, is a heavy bike with some nicer parts than it started out with.
If you are insistent on keeping the bike, don't limit yourself to ebay for parts, the UK has an incredibly competitive market for bike parts, CRC, Wiggle, Merlin, Woolyhat, Winstanley and many others to source parts from, but you still won't get better value than a complete bike, check out
http://www.paulscycles.co.uk/ to see what you can get.
For going from 8 to 9 speed, this is a difficult one at the moment, 9 speed is rapidly becoming obsolete, at the high end, shifters are the first to go, but below Deore 9 speed should be available for the next few years.