Paul, would I be right in thinking that you had your Secteur before your Roubaix and how different do you find the ride is between the two?
I still have it now, and its a cracking bike. I use the secteur for commuting and wet weather (as it has guards) and the Roubaix for Best.
Which one will be best for you is something you will need to decide for yourself. If you intend to commute then the secteur has rack mounts, the guards would fit either as they clip on to an attachment that you fit behind the brake calipers. Also, being ali I think it would be a bit hardier in the rough and tumble of the bikeshed.
If you are after a sportive bike then the Roubiax is better. Its not something you will notice on a 10 mile test ride but it is less tiring as the miles roll on.
That's said, the secture is a very capable mile-muncher and I found that one of the specialized Pave seatpost helped remove some more road buzz, and if you can get one the new seatpost does provide even more cushioning. (I have one on the Roubaix and have used it on the secteur too - a noticeable improvement in comfort but are in short supply. Link:
http://www.specializedconceptstore....ts/road seat post/COBL GOBL-R Carbon Seatpost )
So, to answer your question... despite them being the same geometry the roubaix is easily the better bike. Smoother, feels more planted (using the same wheel and tyre combo) and less tiring.
If you can afford itand plan on doing distance then the Roubaix is worth the extra. If you are commuting up to 20 miles each way with occasional longer rides then the Secteur would easily do that, especially with a pave or Cobl-gobl-r seatpost.