Is it bad to have 2 URL for the same website?

From the stand point of maintenance it is easier to create 1 site with a URL redirect from the second URL. From the perspective of SEO it is better to have two separate sites that are optimized to the narrower niches. The best solution is kind of a hybrid, you use the same back-end with different front ends, so that all of the meta, titles, tags, images etc are SEO'd to the Nth degree, relating the the specific niche. It all comes down to execution. You can simply create category pages that SEO very well for the narrower topic and send all advertising and links for the category directly to them, but having a URL with the keyword in it will always rank better... I tend to buy MANY urls for every site and p through.