8 sp to 10 sp upgrade

quite frankly, it seems like a waste of money to me. 550 dollars is quite a lot of money, and it will probably cost that (or maybe a little less). Unless of course you feel you're lacking in gears in your rides.

8-speed parts will probaly be sold for a couple of years to come, so I would wait at least until you really need to upgrade...(eg when you need new wheels, or when you have problems with your shifters)

On the other hand, I find I always like biking more when I have new materials. So that would definitely be a good reason to upgrade....

(good luck)

I ride a 10 speed Chorus. It's nice, but if your 8 sp is in good condition, there are better things to spend $550 on. Some items I would rank higher than two more gears, and probably cost less:

A set of carbon aero wheels (used, of course)
high end Giro helmet and Oakley M frames
carbon aero fork
carbon crankset
Record titanium pedals and new shoes
Cinelli Angel or Ram bars
lotsa titanium nuts and bolts

I like tinkering with my bike too...