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We've only been here since June 2019 and a couple of the windows have needed serious attention for years - the survey mentioned two areas in particular where the wood in the frame is rotten, and we already replaced another window upstairs (rear facing so cheap upvc) when I opened the casement and three panels opened and the top panel and the glass stayed put.
The windows in general are alright but they're single glazed and I feel like better soundproofing would be quite a large improvement in quality of life. But also a big investment.
Small bathroom done cheap or DIYed would make your life better, repay its cost, and help the place sell quicker I reckon. If it currently looks like it needs replacement any buyer will be pricing that in, and it'll put off a lot of others.
What state are the windows in, and how creaky are the stairs? If they're currently off-putting, tarting them up is worth it to avoid that - the windows especially shouldn't look as though you've been avoiding maintaining them.