That Roubaix with Apex, by all accounts, is a pretty great bike at a very competitive price-point. I just went through the same process recently, with the same basic starting point as you: already with a decent enough bike with a couple thousand miles on it, and getting the itch to move up to something better.

A $2000 budget gets your into an excellent range of bikes: 10 speed, full carbon, excellent bikes. The Specialized Tarmac and Roubaix are both great bikes in the Elite trim, the SL2 frame is no slouch and Apex is great kit: Apex gives all the same functionality as Rival and Force, it just weighs a bit more. But functionally, it's pretty much identical. Ride the Tarmac too if you can, I was surprised how much I liked it when I rode it back-to-back with the Roubaix. I was expecting to like the Roubaix a lot more for long, comfortable rides, and the Tarmac honestly surprised me, I liked it better with the same wheels and kit all around. If you like the bike and you like the shop, you can't go wrong with the Roubaix or Tarmac.

My older bike also has the Specialized CXP-22 rims with generic hubs, they've held up very well to me. I started riding them at ~250 as well, and they've been fine.

Depending on how long you're willing to wait, you MAY be able to get an even better deal pretty soon, as the 2012 line-up may be out soon. Of course you risk not being able to get a left-over 2011 in your size or in the trim-level you want, and you miss out on all the riding you could be doing in the meantime as well. I'm sure they'll have a similar bike at a similar price-point next year as well. The 2012 paint jobs will be different too, which could be better or worse for you.

$1800 is a fine price for the Roubaix, my local shop sells them at 1900+tax all the time with the APEX trim level. If you can be patient, you may be able to score a great deal in the near future. If you're not patient, that's fine too, you can't go wrong.