As a long-time x-cart user myself, I would advise you not to put the redirect in place. X-cart's dynamic pages are very SEO-unfriendly due to the number of header redirects that take place the first time a customer enters your storefront. I'm running an older version, but I don't think they've stopped using the multiple header redirects on the storefront page. Our dynamic x-cart pages have never done very well in any of the engines and I suspect it is for this reason. If you set up a webmaster account at Google and check your sitemaps and spidering stats you should be able to see the x-cart pages that Google has trouble indexing. Unless you can verify that Google is not choking on your dynamic store pages I would nix the redirect idea for now.