Is there any point to me joining the union if I'm ...

The benefits of union membership are, of course, maximised when you are part of a highly unionised and well-organised workplace. However, this does not mean that you shouldn't join if you are the only one as:
Firstly, there are benefits which you can enjoy even as a single member in a workplace where we aren't recognised by the employer. You still have access to the support structure of the union (ie its officers, research and legal teams) to help and support you with any work related issues you might have. Current legislation allows for you to be accompanied in grievance and disciplinary hearings by a union official irrespective of whether your employer recognises us for negotiating purposes. Should you not wish an officer to attend, you will still have access to the information and support you need. Similarly, should you have a serious issue which requires legal assistance, that is still available irrespective of the size of membership in your workplace.
Secondly, even in today's best organised unionised workplaces, somebody was the first to join. If there are issues affecting the rest of the workforce and if some of your other colleagues want to join us then we can come along and meet you. We can discuss the possibility of organising at your workplace and eventually, depending on the strength of feeling and union support, look at attempting to get recognition with your employer to negotiate on the workforce's behalf.
Finally, there are a range of fringe benefits to membership to which you would still be entitled.
Union membership is best utilised if everyone joins but, as mentioned, you would still benefit individually and, who knows, maybe you're the first in a future of union organisation at your workplace.