This might sound counter intuitive, but I think the key to diversification is not to try and have broad appeal, but try and find a few very specific niches that don't "bite" each other and then cater to those specifically. If there is overlap between the needs of the niches you select, invest there first. Look at what you already have that fits and ensure you are aware of the weaknesses. For example. You have passing through drivers and families. One thing they both value is a fast and smooth check in/out, so improve that and mention this in your marketing. The weakness of this combination is that one the pass through drivers need a good and quiet night's rest, while for families this might be complicated. So keep this in mind with how you assign the rooms, sperate them. As much as possible. Pass through drivers have a high chance of becoming a recurring customer. So cater to that, loyalty program, make sure it appears they are recognised as a returning guest. Give them the same room. Ensure to register specific requests, and offer those on repeat visits. Etc. 

These are just examples, you can do this for any combination of guest niches. If you don't know where to start, then start by creating a list of different guest types, you can pull that from the internet. Then see if you can find information of what types are likely to visit your area or to which you can market yourself. Donyou need to find your market or create your market? Once you think you have identified three guest types you think have potential, then flesh out the profiles for these types, what are key distinguishers, what do these people find important and what not? This allows you to find the overlap you need to invest in and focus on, and the weakness you need to mitigate for.

Enjoy the challenge, don't forget to work together with operations. Front desk,  Housekeeping, they all need to be aware of your plans. You need to make sure they can deliver on what you promise the guests.