It depends on you, how much key phrases you want to optimize?
IMO, if you use a title and description for directories then make a new title and description for link building. It will help you to optimize both the key phrases.

My opinion is that rather than looking for a short-cut to boost your link popularity with directory submissions and gathering incoming links of little value you should instead create web pages that are worthy of being linked naturally by other webmasters. This strategy will not only add value for the Internet visitor but your web pages should also be more rewarded by the search engine (for letting your links build naturally).

canadafred, has suggested a nice way to get backlinks if you want to build the natural links.

IMHO I'd suggest you use both of the great methods suggested above regardless of whether you regardless of whether you want natural links or not.

This is very true, You must have quality content on every web pages that you will create..

Yes its always recommend to change title and description. More you change more will be love for your website by google.

how many keywords do you have, you can change your title has many keywords you have but not necessary to change description.....

Didn't understand your reply.

The main thing in a backlink is its anchor text. It must contain your keyword phrase. Suppose you decided to optimize your website for a keyword QUICK REPLY. Then you can use some other forms of this phrase. Write quick replys, quick replys posts and so on.