Do a few things well! Why we only do Drupal.
It's very difficult as a small web agency to turn down work, and 5 years ago we found ourselves in a position of trying to be everything for all people in order to not turn down work. It was exhausting! We did a bit of Wordpress, a bit of IT support, some PHP, some Joomla and a bit of Drupal and we were struggling to be really good at any of them. We were meeting expectations from our clients but internally, we just weren't quite satisfied with our work. We felt a bit stretched and that our knowledge was thin in some places. We were mediocre at a lot of things, and excellent at nothing. We wanted to be excellent and we wanted to be experts.
So we took the decision to specialise. It was a difficult decision and even deciding on how and what to specialise in was difficult. We evaluated lots of CMSs and lots of ways of working and we decided then, that Drupal was going to be big. And also, that we were going to be a part of making it bigger and better. For us, that meant working within the community to commit code back to Drupal and using our marketing to re-inforce the Drupal is Awesome message.
It is very hard for an agency to say no. It is very hard to say, "we don't do that." One of the laughs I've always gotten from the tiny little 3 person agency is that they say that they can do everything - a bit of website building, some design, some wordpress, a bit of shopping basket systems. We've grown to 15 people and we are adamant that we can't do everything - we can bring in trusted partners that we work with on a regular basis to support our Drupal work but we're not going to divide our attention to look at rolling out Joomla, Wordpress, Sitecore, Umbraco etc solutions for clients. It's very stressful to not be 100% sure of the work that you're doing and we prefer to be 100% confident that we can deliver what the client actually needs.
We're pretty glad that we did choose to specialise in Drupal. Drupal has grown and grown, and we've grown alongside it. We've moved from building small to medium sized websites to building more and more complex online products with a focus on high availability, super-fast solutions. No longer are we over-stretched and underperforming, we've dedicated our teams to knowing as much about Drupal and building good Drupal websites for our clients. Not only that, we're now doing Drupal peer code reviews and Drupal Training to support our development output. We have reached our goals of being the Drupal Experts.
Overall, we couldn't be happier we made the decision to go with Drupal!