On the groupset I think it really depends on what you want to spend and how serious you want to get with the biking.
I believe all groupsets work just fine for the leasure/amateur racer and really only a pro needs a higher end (shimano dura ace/sram red/campy record).
BUT there certainly is a difference in shifter/shifting feel when it comes to the different quality of the groupsets and if you have the money and you do like quality/high end parts on your bike, I'd say there is nothing wrong with a higher end groupset. Hell, I sport a Shimano Dura Ace/Ultegra mix on my Trek bike myself and I love the smoothness of the shifting, but I can ride my '93 steely with a 15 year old 105 groupset almost as fast as my new Trek... almost
. The shifting is definitely a world of a difference, but so are 15 years in between the groupsets. But for a century or longer distance ride it really wouldn't make a difference since shifting is down to a minimum on such distances. In a crit race on the other hand where you continually adjust your cadence to match your strategy/attack/draft etc it is much more critical on how well your groupset works. I certainly would not race my old bike with downtube shifters in a crit or a road race.
Also wheels:
The wheel weight is only important for fast/explosive acceleration and doesn't matter so much in long distance rides. Again light wheels are good for crits/road races and mountain climbing.
And I ride my Trek during events and crits, but I used my steely last year for commuting to work (30 miles on way). For ultra long distances I would take my steely, because I have the beefier wheels on that one (36 spokes front and rear) since durability matters when you go beyond 200 miles in one sitting.
But that's just my opinion
Thomas