Is the Shimano 105 really worth it?

The lower level Tiagra and Sora components are perfectly functional, especially the newer stuff. However, 105 components are the first level of parts that are considered race-level (if that's worth anything to you ).

Also, traditionally the Tiagra / Sora parts have been 9-speed, which can cause some compatibility issues if you end up switching parts out with 10-speed components (which is anything 105 and up).

If it was me, and cost wasn't too big of a factor, I would definitely go with the 2.1 with 105 parts. However, it's not like you will hate life with Tiagra or Sora stuff - it works fine.

I think you answered your own question.  Get the best you can afford.

Is it really worth it?  Of course- the answer to that depends on a lot of things, but overall:  YES.  105 is good stuff.  Ultegra is worth it too.  As for Dura Ace- it's hard to make a financial vs performance case for DA, but you sure will see a lot of people using it.

That's actually the easiest part for my wife and me considering she thinks budgeting money is fun and we have no children. We're just kinda paranoid when making larger purchases in ensuring we are making the best purchase possible. I think we're definitely going to go with the 2.1 especially after taking into considerations the wheel upgrades in addition to the component upgrades.  

I noticed you're the race direction for the Sugar Man Triathlon. We are actually from Houma, LA and visit regularly so I think we will definitely try to fit this tri into our schedule!

Cool. Remind me after registration opens and I'll hook you up with a discount code.

Where are you shopping bikes?

Sora<<<<Tiagra<<<105<Ultegra<Dura Ace

The marginal upgrade value from Tiagra to 105 is still great; much greater than from 105 to Ultegra, or Ultegra to Dura Ace. 

I think Shimano 105 components are a pretty big step up from the lower tier components. If you plan to ride a lot, then I would say, yes, 105 is worth it if the cost is not astronomical.

Usually trickle down idea doesn't actually prove true, but in this case some of it is.  

Note that Shimano intentially keeps differences between the groups.  Their groups can be split into two families.  2200/Sora/Tiagra/105 aimed at the recreational rider, and Ultegra/Dura-Ace Track 7700/Dura-Ace 7900/ Dura-Ace Di2 7970.

Last year Shimano introduced the "new 105" set which contains a number of features from Ultegra but excludes some of the more weight-weenie oriented features like carbon levers.

 The new one is 105 "5700", and the old one is 105 "5600". 

BT on "Shimano 105 or Ultegra" from Dec 2010 (reviews the 5700).  This article well details the differences, but conclude the Ultegra is always better.  Sort of lame.

http://www.beginnertriathlete.com/cms/article-detail.asp?articleid=2151

And several more which really like the new 105 5700:

http://www.bikecyclingreviews.com/Shimano_Group_Sets.html 

http://www.bikeradar.com/news/article/first-look-new-shimano-105-road-groupset-24923

http://www.cyclingnews.com/reviews/shimano-105-2011-groupset

So if you're interested in 105s, be aware of the old 105 vs. new 105. difference.