What should your site see when it comes to new visitors versus those returning for another visit? As with many questions, the answer isn't cut and dried. It depends on how you're marketing your site, it's growth rate and the content you present. Long term, you want a high rate of returning visitors. The only way you can keep a site visitor around until they're ready for a real estate transaction is to provide content that they find valuable on an ongoing basis. They will come back over and over to either search listings or to read your latest statistics or area information.
Particularly with a new site, you may be doing some Pay-Per-Click advertising to bring visitors. If so, you hope that your new visitor percentage is high, as that means your PPC is working. Along the same lines, if your SEO is working, you will always be luring new visitors from their search engine queries. With a blog, your new visitors percentage should always be higher than with a static website. This is logical, as you are always creating new content if you're blogging regularly.
However, once you've lured the serious real estate visitor, they may come back over and over to use your IDX or other MLS search page regularly. Many will visit daily. So, if this is working for you, you will see a high percentage of returning visitors. If you're not somehow capturing their email address for a newsletter or getting them to subscribe to your RSS feed, it still may be traffic that isn't resulting in business.
See how a simple question can result in a really complicated answer? I'll simplify the answer for you. There isn't one that fits every site. As you can see, the content you're providing, the ways in which you are promoting your site, and the age of your site all influence the answer for your site.
Here's my take on it. You want both to be increasing over time. The ratio of one to the other is much less important than the increase in both numbers over time. Keep up the great SEO and PPC for new visitors, while encouraging RSS subscriptions and email newsletter sighups for your ongoing content and returning visits.
