Specialization is good. Focus is good. Finding a niche is good.
Generating revenue is great.
Anything a customer will pay you a reasonable price to do, is something you should do. Your customers want you to deliver outside your normal territory? If they'll pay you for it, fine.
They want you to add services you don't normally include? If they'll pay you for it, fine. The customer wants you to perform some relatively manual labor and you're a high-tech shop?
Only do what you want to do and you might build an okay business. Be willing to do what customers want you to do and you can build a successful business.
Be willing to do even more and you can build a remarkable business.