Love all the debate here about baths! We're in the process of renovating our house (moved in 2 years ago) and we're thinking really carefully about the improvements we make - both in terms of whether we'll get maximum value from them, as well as for potential resale value. Our bathroom is small and only has a shower - albeit a fairly large one. We debated whether to install a bath, but ultimately decided to incorporate a freestanding bath into our master bedroom instead.
The bedroom is large, but an odd shape and dark, being around 20' long and 8'6" wide with a window at the far end, but zoning it into two separate spaces has really made it feel less like a 'corridor'. My view was that if someone who buys our house has no use for the bath, it's a lot less hassle to de-install it from the bedroom than it would be from the main bath(shower)room.
The most 'wasted' feature at the moment is the entire wall of glass in the lounge being two large patio doors with fixed floor-to-ceiling panes on either side - I hate it! The room boils in hot weather and you have to keep the doors open all day, with voiles pulled across to provide shade. The windows were almost brand new when we moved in, and replacing them isn't in our immediate budget, but I wish the previous owners had thought about the practicalities of not having some sort of small opening windows, too. I love fresh air all year round, but you can't keep a big door open all year round.
Our garage is also a totally wasted feature at the moment - it's DiY hell and we can never find a single thing in it when we go hunting for a spanner or any one of the fifteen tape measures we've accumulated. I can't wait to Marie Kondo the shit out of it at some point.