Bar End Shifters

What kind of bike do you have? If you have a road bike with aero bars on it (sounds likely) I would not change anything with the front end. 

What would you be gaining by making this change? The ability to shift while on the aerobars. Maybe you'd lose a little weight on the bike. That's about it as a practical matter. Some retro-grouch types argue that you gain the ability to shift in friction mode with the bar-cons, but I don't know that this is of any practical importance to a triathlete.I have barcons on my cyclocross/winter frankenbike, and I really like them, so I am not anti-barend.

What would you be losing? A couple of hand positions from the drop bars. You will lose the "push-button" shifting of the STI system (I'm assuming you have shimano). It's also possible your fit will be a little worse than before. Then there's the cost of the conversion. Additionlly, you mention group rides, and fair or not many folks look askance on riding a paceline with someone with a full-on TT/Tri front end.

If you make the switch you won't be any more aero than you are now. If that's you in your avatar pic, you look to be in a pretty typical "road bike with clip-ons" position. You might be able to tweak your position by playing with stem lenght and height, but the reality is that the frame is going to define the limits of your position, not the bars. I say spend the money on the engine.

Aero position has minimal advantage under 18mph and virtually none under 15mph.  If I can maintain 15-18mph then I certainly don't consider it a hill...unless I'm going down it

Okay, I have to disagree with THAT statement...There are many days here in Texas when I am going 10mph pedaling directly into a huge headwind...if I sit up, it gets harder.  You can get an advantage in aero under 15mph.

To answer the original question...I love my bar end shifters and the bullhorns.  You can quickly get used to climbing a hill in the bullhorns and reaching over to shift.  At the same time, you can also get used to being in clipons and reaching to your bike handlebars to shift too.  Go ride some tri bikes at the LBS.  I do find the bullhorns more comfortable than traditional brake hoods...not sure why.

Well, you're twisting what I said (or at least the intent) a bit there.  Riding 10mph into a 15mph head wind would be analogous to riding 25mph with no wind.  So, technically it's not your ground speed that is important but your "air" speed taking head winds into account. 

Did I just read airspeed? Speaking of speed man, now we're flying!!!

Just kidding, but you knew that I'm sure

My experience, in addition to all of the other stuff said is this.

I found that I am always in the gear that i need to be in to keep my cadence up because i can pop through my gears easier with the shifters on the bar ends. no mooving to the hoods to shift, just low and aero and stable.

yes, climbing sucks a bit, but it can be done.

i won't go away from bar end shifters anytime soon.........