Branding is probably the most subjective marketing topic there is. It really depends on how big you plan to grow, what your corporate footprint is for targeting business, and what kind of marketshare you think you can go after and obtain. This form of marketing is probably the least measurable direct ROI because it mainly builds awareness.
Awareness is necessary to drive sales and help gain customers, but at what level? All the Fortune 500 brands and even the Fortune 1000 brands typically spend millions to tens of millions in making their target audience and demographic know who they are, what they offer, and what are the new products they offer. The bigger you get, the more important a branding campaign becomes. If you are entering new markets or geography, a branding campaign is definitely a component of that expansion. The biggest ROI you get with branding is the ability to measure awareness - how many more people now know you exist that did not before the campaign, especially in your target market,s industries, and demographics.
Branding is also done differently if you are consumer oriented versus business-to-business. You have to understand what forms of media will drive awareness and make sure the messaging strengthens your position in the eyes of your audience. You have online, print, direct mail, email, billboards, interactive, your web site, trade shows, radio, and television to create the right media mix that will give you the best awareness when the campaign is finished. There are also local, regional, and national components. You might look to test in a few markets to 'own' them before you try to take your branding efforts to a larger scale.
We can help you navigate these waters and determine what form of marketing is best for you, do you really need to be concerned with awareness/brand based on your corporate goals, where you should start, how much you should spend and why.