You want to change your website's domain name, why? Is it because you want one with your business' relevant keywords in it - simple or maybe not.
You probably started out with a funky or quirky domain name, say:
But now a few years down the line you realise you want to actually generate some money through the website, its vanity role is over. So, your business is selling blue widgets, therefore you think the optimum domain name would be:
You find your lucky enough to acquire this new domain name, so it's plain sailing now.
Unfortunately not, and it's not that an optimised domain name isn't any good anymore, it sure can be, no matter what Google's Matt Cutts says here 'Matt Cutts Talks Down Keyword Domain Names', an optimised domain name can benefit Google SERP ranking. No, the problem lies with the duration of the switch over; even if you carry out the domain name switch in Google Webmaster Tools, and then create the 301 redirects from old domain to new domain - this can all take 3 or more months for your site to get back to where it was in SERPs. I mean would you only open your store for 1/2 of the day for 3 month's hoping at the end of 3 months it'll double its takings - is this what you'd be expecting, here I tend to listen to Matt Cutts, because I doubt the switch-over will get you storming to the top of Google SERPs.
Naturally all this depends on the size and relevance of your website, if it's still an under-performer then go ahead and make the changes, but if its got a pretty good Google PageRank, well I'd pretty much leave it where it is, and concentrate on its usability, SEO and marketing to generate that increase in income you desire.