Since the shifters are the biggest ticket item, if you were ever considering an upgrade, now's the time to do it. With 10-speed stuff out, there are lots of good deals available on 9-speed components.

Rear derailleurs guide the chain by the center so they don't care how wide the chain is or how many cogs the cassette has. Your present derailleur will work fine. Front derailleurs guide the chain by the sides and are specific for the different width chains required for different numbers of speeds. The difference is so subtle that an 8-speed double front derailleur will work for a 9-speed. I've found it necessary, however, to get a 9-speed front derailleur when upgrading a triple.

Other than the prestigue factor how much you prefer the extra cog that 9 or 10 speed provides depends on the flat road gears that you most commonly use. If 53/16 is your favorite flat road gear, a cassette that lacks a 16 will suck. If it was my bike, I'd figure out what specific cogs I needed and choose a drivetrain that provided them at the lowest cost.