A client has a site since 1999 with a domain consisting of two, very descriptive of the business, words (let's say dog-toys.ie). In about 2001 he decided to change to dogtoys.ie (was running radio ads and figured the dash may add confusion to the site name). So without thinking too much about it, I just parked dogtoys.ie onto dog-toys.ie. Also, for both domains, we have not made www canonical so www.dogtoys.ie/example.html or dog-toys.ie/example.html are the same page.
We have read many times that Google etc do not like this, however the site has performed fairly well SEO wise for the last 10 year and the client and I are torn between leaving things as is, and fixing it to make www.dogtoys.ie canonical via mod rewrite (or would the dashed version offer better performance?)
Thanks in advance!