There's a high probability of brand confusion with MarriageCenter.com. The latter domain is shorter, and shorter is usually more valuable. But, in any case, whoever develops one domain needs both to rest easy. I can imagine an end user paying a $1000 plus or minus for this domain. But that's not a guarantee that they will come along and buy any time soon or ever. Most domains sit on the shelf. It's the minority that sells during any period of time. Once you get an offer, work with it.