On the other hand, if you keep your 8-speed shifters and cassette and crankset, you can upgrade the derailleurs. Derailleurs don't care how many gears there are, the shifters determine that. Just make sure the shifters can handle the range of cogs you have. If you wanted to upgrade the shifters to 105, you'd have to look for an old 105 shifter from the days when 105 used 8-speed (guess it's now 10-speed) or convert to 9 or 10 speed.
Oil is good, grease is better.
2007 Peter Mooney w/S&S couplers/Terry Butterfly
1993 Bridgestone MB-3/Avocet O2 Air 40W
1980 Columbus Frame with 1970 Campy parts
1954 Raleigh 3-speed/Brooks B72