People interested in those keywords will search for them as well as clicking on them in other tweets. As a result those who share your interests can find your tweets much more easily. So using them is a good idea, and can significantly increase the speed with which you build your network.
Use popular, relevant hashtags
As you get increasingly active on Twitter you'll start to realize which hashtags are used most often. For example, the most popular hashtag for politics junkies in Australia is #Auspol. As well as learning which hashtags are best for your content simply by osmosis there are various sites that offer hard data about which ones are used most often such as Hashtagify.me.
Hashtags are particularly useful for those with a geo-specific focus. The obvious one to use for this city is #Perth. On my Twitter account for this site I used to include it in many tweets where appropriate. That definitely helped. But because it was so popular, it tended to get buried very quickly.
Variety and specificity help
So I altered my approach a little and became more specific: For example I started posting photos of local restaurants and cafes using hashtags like #Perthfood and #Perthcafe. If I search for those I see that I'm hanging around at the top of the results for quite some time. Since doing this I've noticed that people are now following me at a faster rate than before. (This may be due to other factors, of course. But I don't think so.)
Of course less people search for hashtags like this but they make you findable for longer, and because of their specificity draw people who are more likely to want to connect with you. So they are very much like the "long tail keywords" that search engine optimizers talk about.
Needless to say these "long tail hashtags" don't have to be geo-specific. They can just narrow the focus of a particular subject. For example, instead of always using the hugely popular #socialmedia I've been including ones like #socialmediastrategy, #socialmediatips, and #socialmedianews. Whatever field you're in there will be ones like this that you can utilize to quickly expand your reach on the site.