you never recoup what you spend on improvements
This isn't set in stone imho. We've been on both sides - 1) restored (proper high end, period restoration, not mere renovation!) a lovely old Tudor house in a less than perfect location, sold up three years later and not only did we not recoup money spent on the work, but we sold for considerably less than we'd purchased for. All the EAs we had round said we had merely made the house more saleable and to prove the point we went SSTC within 10 days, when neighbouring (poorly & non-renovated) houses were taking upwards of six months.
Otoh, 2) did a similar restoration job on a rural Georgian house that was previously unmortgageable. When we sold three years later we expected to recoup the extension costs, but not expenditure for other 'improvements' (windows, bathrooms, flooring, rewire etc etc). However we got all our investment back and some. Again sold very quickly compared to average for area.
OP, in your shoes I would want to sell and move, but it does depend heavily on how quick you can get yours listed, how fast it will sell and how long the other house will hang around.
When we bought this house in 2014, we viewed it before ours (the Georgian one above) was on the market. Put in an offer that wasn't taken seriously, so we got ours listed, went SSTC in 5 weeks and put in second offer that was accepted on the new house (but that was in a very slow moving area). Moved in about nine weeks later 