As much as I want to keep out of this I'd say I can't see a 'simple single easy' move to improve, like it's all or nothing, if you've really got time on your side (and allowing the stresses of life to build up while storing 'things for the project') start the research to what is needed to make a refit possible.. ironically if it were at a less finished state you'd be at a better starting point

I wouldn’t spend any/much money on it at all, until you can afford to rip out and replace the whole thing.

I was in a similar position for years, had a nasty, old & busted bathroom backing onto the kitchen (en-suite kitchen/bog was kinda cute, eye contact whilst tossing the sausages). Kept fantasising about re-doing the grout or whatever, then the shower collapsed, flying ants kept hatching from inside the foam insulation around the water tank etc. Really glad now that I did fuck all till it all got dashed in the skip.

I'd just paint the panel. Maximum impact for minimum effort. Painting the skirting, door, ceiling etc can also be a good refresh for not much effort/cost.

I'd be tempted to look into removing the handrail as I think that would make a big difference but might be a faff.

Maybe the shower screen if you can be bothered but I'd say that's getting into diminishing returns.