Blenny, I would be extremely cautious about redirecting another site to your site, even if it's ranking well now. There are a lot of issues that you need to consider, especially given the fact that all of the factors (links, history, content issues, etc.) are going to be passed on to the new site.
You'll need to look at the site's link profile in depth to make sure that the site isn't ranking well for a particular reason. The site could be ranking well right now because of certain links to the site: but Google, for example, has not penalized those links yet. I've seen sites that have a lot of low quality links that help a site rank: but when Google gets around to re-analyzing the site (i.e., Google Penguin), the site then literally falls out of the rankings and becomes penalized.
If it's a new site that you recently bought, are you sure the former site owner didn't just pump up the site's rankings in order to sell it? Perhaps they used techniques that would eventually get the site penalized?
I don't like to sound pessimistic here, but you have to look in depth into the site before you redirect it to your current site. Your current site could end up banned or could end up with a penalty, especially given the fact that you say that the content isn't that great.