SEO is an expensive business and a lot of money can be lost trying to compete with firms that invest large amounts of cash.
Email marketing is not really effective as most people just regard it as spam but I'm not saying you can't have some success with it.
I'm sure as you know the hosting business is beyond saturated, building a firm and seeing steady growth is not easy. You should do everything you can to help your SEO efforts a lot of which will not cost you a penny. Forum's are excellent they put you in direct contact with potential customers and get your brand known.
In my opinion SEO is a very expensive marketing strategy early on which is exactly why most hosting companies spend most of their time doing paid marketing and later on after the profit has grown they start spending their budget on SEO which is more of a long term plan that could take quite some time.
I think almost online business need SEO strategies. Not only for hosting industry but also for many ecommerce fields. Well-optimization in SEO will drive you many quality and organic traffic. These types of traffic will have a higher conversion rate then you maybe get more lead/sale on it. IMO
If your running a smaller company SEO is just not worth the investment if at all investing. Usually smaller host stick to forums and what not using backlink and just tip and tapping into the SEO style. NowADays with all this Social Media and what not you really don't need to put any money into SEO just know how to work with it. Before going into or spending any money on SEO one should always read up on the latest news and gain loads of knowledge before letting any pennies go.
Of course hosting providers need SEO and just like everyone else, it is important. I think that for hosting providers it can be tough to gain ground with all the competition out there but if you ignore SEO then you will be missing out on an opportunity.