I'm starting to lean back towards a TT over a road bike

A TT bike sounds fine for your intended uses.  

That said, and this is just my opinion...your intended uses are probably why cycling doesn't interest you.  Just sayin...I'd be bored out of my mind too if all I did was ride flat trails by myself.

Yep. If all I did was ride a flat trail (and there is one fairly close to my house), I know I would ride a whole lot less than I do. Along with that, if all I had was a tri bike, I'd also ride less than I do...

Hello, I have, and did so.

Well...it's not really a group ride if you drop the group.  

I started on a road bike, got in an accident with a truck (the truck won...) that totaled my road bike.  I went back and forth about road vs tri bike when I was ready to replace it and buying the tri bike won out.  It is a decision I've never regretted. 

A couple years later I'm considering getting a road bike, but still haven't pulled the trigger.  I ride with a group of triathletes, so I still ride with people, but I get to do it on my tri bike.  Best of both worlds for me.

If I weren't that into cycling, I'd go TT.  That's how I initially went.   Then I got into cycling more, and bought a roadie, then bought another one this year that I love.  I love all my bikes now 

But back to your point    for now I think TT's the way to go

Yes...and the rules dictate that you have to buy another bike after that anyway...so plenty of room for a roadie later.

That has actually never happened.

I lean towards just getting the tri bike here as well. I've only used the tri bike for the last couple years and had a heavy percentage of time on it the couple before that. I'm only using the road bike now because of a snafu in getting a new tri bike. I do get into group rides every now and then (maybe a couple times a year?), but a very large percent of the time I'm on my own. The groups are also tri bike friendly. The bike events I do are as well.

Very true.  105 and/or Rival is high quality.  Especially for a tri bike where the minor differences in shift quality aren't as apparent as they are on a road bike.  Both have already recently released their 11 speed versions which should start showing up on new bikes next year. 

I'll go one better, I bought a 105 equipped BMC TT last year, which actually meant a tiagra front derailleur (shudder).  I meant to replace it, but never got to it, and you know what?  Works just fine..... 

My first bike was a $700 Trek, very entry level, alum with carbon fork and seatpost, Tiagra components, etc. I rode that bike for a few years, did my first two tris on it, then decided I wanted to step up to HIM distance and thus justified a new bike (in my head, not reality ). 

I had tried the clip on bars on my roadie was never happy with the fit, so I decided on a TT bike. Bought my Cervelo P2C in 2009 and absolutely loved it. I rode the TT bike almost exclusively from then on as it was just a much better bike, full carbon, Ultegra, etc. I eventually upgraded my roadie to full carbon and 105's. I would say my riding changed to 25% roadie and 75% TT bike at that point.

Up until last summer I never rode in a group, always by myself so the TT bike worked just fine for me. I honestly didn't really need a roadie during this time, I just wanted one and got a good deal so I bought it (made the wife real happy). Last summer a new LBS opened up in my town and offered Wednesday and Saturday rides. I jumped into the group ride fray last year and after the first few times of getting dropped like a bad habit I got things figured out and I absolutely love group riding. I have made some good friends, had a ton of fun, and become a much better cyclist than I ever was on my own. The best way to get better at something is to try to keep up with someone who is much better than you. 

Anyway, last summer was all roadie, never touched the TT bike. This year I had an IM in June so I switched from roadie back to TT in March, rode the TT for most of this summer. My riding buddies are ok with me riding my TT bike with them, I keep a safe distance and take a lot of pulls when on the TT, so I still did a lot of group riding this Spring. The TT is not near as fun in the group as the roadie, it doesn't handle was well, it is a little harder to sprint hard on, and you can't draft real close in the paceline. Another not so fun aspect is your face is at everyone's butt level, hard to carry on a convo during warmup or cooldown. Now that my IM is done I will be going back to the roadie, just more fun in a group. Will use the TT for Tuesday night TT's and perhaps an Oly or too this summer.

If you really prefer to be alone or have to be alone due to schedule then yes, go with the TT bike, you can always pick up a cheap roadie later. There is a guy in my group that can put just about anyone in the hurt locker and he rides a 25 year old bike, you really don't have to have a high end bike.

I like your strategy on the level of bike too. Full carbon with at least Ultegra is a great way to go. My 2008 Cervelo P2C has full ultegra and it still works great, is plenty fast and I love it. No thoughts of upgrade on the horizon for that bike, it is still much faster than I am. I'd say you would be plenty happy with a bike on the level of the P2C from any brand for many years. I got some Zipp 404's for my TT bike this year and it became a whole nother animal, very fast and smooth.

 No reason you need to change from a road bike to do a HIM, lot of people on road bikes at the one I did recently.

You can do both of these on a Tri bike anyway, so mute point.

You say that now.....but wait until you have your Felt DA, you'll find any reason to ride that bad boy!!

 I think the TT bike is the right move for you given what you've said.  No reason you can't use it on the odd occasion you get a group ride opportunity, or want to hit some hills.  (talk to the group first though before you rock up with the TT I know some can be funny from discussions on here, although I have never had an issue).

And the all important, the TT may not be a lot faster, but they darn sure LOOK a lot faster :-)