prasanth5 is correct too. Quality backlinks are important but be very careful about where you back link from. Paying for Back links is against Google's policies (dont take my word for it, take googles). Google considers it Gaming their system to pay someone for improving your sites PRV rankings (do not do it). Try to get Quality back links from services directly relevant to your business model (Associations, trade groups, etc) for the best results. Many such professional associations are FREE to get them to link back to your site, Some are not. The easy way for quality backlinks to improve your regular business site is to have your site listed (which would be another PAGE) about it at various directory listing services. Google indexes PAGES (not back links or text links). For Google to start Penalizing PAGES about your business would mean they would have to Penalize Manta, Linkedin, Yellow Pages, Amazon, Ebay, Facebook pages (you get the idea). In the end, Pages about your business will always win out in Google and can accomplish all your end marketing goals in a single step PRV, More pages in Google, More Keyword rich content Google can use to help find you. What else do you need?
Aside from updating your directory you can always do marketing to gain visitor and all monetization methods will follow... I don't have directory but used to market directories for clients...since its directories for medical practitioner we use paid advertisement where we let them pay for a premium account/advertisement. Some of the directories use cpa and cross promotion way of marketing depends on your visits and leads... hope this helps...