In my opinion as long as your needs are exclusively about looks it’s never a good reason to migrate to entirely different code base. The separation of backend code and frontend site is inherently one of the strengths in web development.
When you you are a lone developer on own project there are roughly three design options:
- Custom tailored commercial design [which you typically won’t have spare mountain of cash for :)].
- Off the shelf commercial/free design, specific to framework used or provided as generic to be sliced.
- DIY design, preferably starting with off the shelf foundation and customizing to your specifics.
You seem to be interested in framework case of option 2, but resource investment you are considering (switching/integrating with WordPress) will be very considerable.
If you operate with money that cost might be better spent on just getting great custom design.
If you operate with time you might focus it on DIY design update. It won’t win design awards, but it will be perfectly usable.
In either case you would have a benefit of individual solution, better fitting your functionality.