I am in a VERY similar situation around the same price point, thinking of selling my place next year as well.
I agree with CowboyAndIndian that "Most people buy a house based on looks."
I am doing the same renovations too. last year I put hardwood floors (over the old tile) throughout the house, and renovated the kitchen with new cabinets, and butcher block countertops. The whole looks of the house completely changed!
Now I need to update the bathroom floors, walls, and vanity. My bathroom is small with a tub, and the tub space is tiled. If you DIY yourself, it shouldn't cost a lot. The bathroom is important so the nicer it is the better. I am also thinking of putting some crown moldings in the rooms, because people do notice that, but I don't want to put something that would be out of place with my price point.
By boiler, do you mean water heater? If it is something really old like 40 years and does cost $8k to replace, that might be brought up during inspection(almost certainly), and the buyers might renegotiate for you to fix it/replace or back out. People usually don't have that kind of cash, the heating coil is the least worry (you'll have cold water and it's cheap at $400) the real problem is, if the water heater blows up/starts leaking it can flood and damage the property, and it has to be replaced.
I have an old electric water heater too, It works like a champ but I have decided to replace it and reduce potential headaches during negotiations. Also, I reduce my risk of the thing blowing up and flooding my hardwood floors.
For the butcher countertops, I used Waterlox Original. I would sand and prep your countertops, tape off any areas that you don't want to get paint on, and get 5-6 good layers (or more). There are a bunch of videos out there that show the process. I would recommend, 2-3 coats the first day(depending on how it dries, than for the next few days, each day do light sanding (take off any bumps or runoffs) and another coat. It will take a few days, but your countertop will look amazing and water resistant for a long time. You will have to have good ventilation in the kitchen however for those days, and ideally you want to have it dry for another week before it gets any heavy use or you put anything on top of it.
Than again if you do just want to refurbish it before sale, you can just do rubbing oil or another less time consuming alternative.