it is easy to get nervous about spending large sums of money on your home. I know, I spent about 95,000 on mine last year. I did have a few crisis about spending that during the build. I was in a similar sized home to you with a similar value. We had loads done (loft room/ensuite, rear extension, new kitchen with appliances, boiler, driveway, patio, all internal doors replaced to oak, new oak stair parts, new double glazing throughout, downstairs loo)
I think now that over the year with all the house price increases etc in our area we would just about make our money back if we were to sell now (possibly a little down, however when we started this I did assume we would be 30,000 down if we were to sell straight away). It was hard however I had to just think about the family benefits, lovely lovely family room, a large bedroom for everyone living here, two bathrooms (how much easier in the mornings!)
Like you we will be here for at least 10 years, maybe forever now as I love my home as it is. So I just think the money was worth spending to have a home to love and enjoy for all the family.
All the best with whatever you decide.