I, like you, have been enjoying my purchase of a new (leftover) trek 2.1 All the bells and whistles at the stores and all the forum fodder is overwhelming and just makes you want to upgrade!... I say this, each item you think you need should have a mileage requirement. If you think you need brakes you may as well ride the bike for 100 miles and then decide if you feel that way. I wanted it all in the beginning. I held myself back and all I do is ride my bike. I'm blown away by the tech in these newer bikes and I can't see making any upgrades until I see something that actually is in need of being "better" or more functional. Also, by waiting, you reserve some of that hard earned cash to be used for any repairs or issues that may arise.

I know for me my secondary purchases have gone like this.

trek 2.1 with a helmet and a $35 cyclecomputer
two bottle cages and two camelback 25oz water bottles. (buy camelbacks insulated with jet nozzle)
floor pump with guage
seat bag with spare tube, c02 inflator, loose allen keys, tube patch kit, exact bus fair (emergency get home), presta valve adapter in case of needing to pump from a schrader pump, and my ID with housekey.
Then I bought my girl a trek skye S mountain bike for our evening rides together.

The list of wants is much larger than what I've purchased but for now this has me going strong. Since I'm still new and working my way to more endurance I don't need all the high end gear due to not being able to ride much over an hour at this point before my big ole' legs turn to rubber.

Good luck with your purchase and your upgrades just don't forget... riding it is the most important and you've already paid for it. Adding more money to it doesn't make the mileage add up, only you do.