If you were to get 50k, what would you do with it
I won't answer that question because my circumstances are very different to yours, so what's sensible for me is different to you.
In your circumstances, I would use the money to try and move from a position where you need to borrow for big purchases to one where you can do this out of savings, as then you earn interest instead of paying it, which makes a huge difference.
Unless your car finance is interest free or very low interest, pay it off. Then save the car payment at least so next time you need to buy a car you pay for it with savings. Also make sure you save for annual and irregular expenses like Christmas, insurance, car servicing/MOT, etc etc, before spending on non essentials like eating out or clothes for adults where you don't need them.
Maybe use some of the money for invisalign and the conservatory, but also aim to save some of it, so get one thing a year for the next few years and save at least a couple of hundred a month towards it.
If you haven't reviewed your finances, you will almost certainly be able to cut some costs and free up the money you need to save for these things, have a look at:
Do a money makeover and potentially save £1,000s - Money Saving Expert
Don't get fitted wardrobes, they're hugely expensive. Get Ikea Pax and pay a carpenter to cover the gaps with MDF/plasterboard if you can't do it yourself and paint it. Looks similar for a fraction of the cost. Google Ikea fitted wardrobe hack.
As for 'appearing tight' if you're not getting involved in rounds and taking packed lunches, you're doing the right thing. As long as you're not expecting others to sub you, you'll save a huge amount of money by not buying food at attractions where it's almost always overpriced, shit quality and at the end of a long queue.