Best seat in the theatre for a show you really want to see, starring actors you admire.
Same, with any bands or musicians you love.
Spa day at a truly luxurious place
Other craft classes: basketry, weaving, tapestry, dressmaking, upholstery
Sign up for a term or two of creative writing and start a novel!
Wardrobe overhaul, maybe with a personal shopper or stylist to help you develop a more distinctive look that feels empowering
A night or two away somewhere nearby that you've always wanted to explore, in UK or Europe. I've always wanted to go to Whitby when the steampunk crowds are there, listen to ghost stories, visit the abbey. That sort of thing (or the opposite, depending on what you love)
Sign up for a book festival or music festival weekend in a genre of writing or music that you love. I went to Harrogate Crime Festival alone once. It was such fun. Met people I'm still friends with years later.
Search for and buy objects that create focal points in your home. I have a bit of an obsession with these. A really stunning table lamp on an antique or ultra modern desk with perfect coffee cup, notebook and pens or beautifully bound novel by an author you love. Or a really soft thick throw and cushions on the sofa, for quiet nights in watching classic films or box sets.