What kind of upgrades to a BMC AC02 hybrid? I bought a hybrid bike about one month ago. It's a BMC Alpenchallenge AC02 Tiagra. Have been having a blast on it to the point of considering to eventually get into road bikes

Full Specs can be seen here:
http://www.bmc-switzerland.com/int-en/bikes/lifestyle/mountainroad-alpenchallenge-ac02-tiagra/

Chainwheel:
Shimano Tiagra, 50-39-30T

Cassette:
Shimano Tiagra, 11-34

Tyres:
Continental Sport Contact II, 35mm

Rims:
DT SWISS R522D

So the question is, if you were to do some upgrades what would you get?

I plan to get a road bike in 1.5-2 years time. In the mean time I'd like to use this one to train (likely uphilly stuff like http://www.cycling-challenge.com/col-de-la-faucille - over 1000m altitude). In terms of improving performance/handling/speed what kind of sensible upgrades can be done for a budgeted $500 tops?

Thanks in advance, would much appreciate your inputs!
The best upgrades would be a set of clipless pedals, compatible shoes, and some nice cycling clothes and helmet. And maybe a good set of lights. You can carry all these over to your next bike. 

Another nice upgrade is a bike repair stand and a basic bike repair toolkit.  

Finally, a good GPS bike computer or GPS watch will set you back a few hundred dollars. 

I think you get the idea. There are no "upgrades" to an essentially new bike itself that need to be made. Only buy things that will encourage you to cycle more (Strava premium membership!) or that you can take with you to the next bike.