My bikes to help,
2017 Giant front suspension, capable but boring.
Roberts White spider with Bonty Forks lovely looking but too nice to be used in anger ??
Kona Explosif, hardcore and much too hard on my middle aged battered body.
1997 Specialized Rockhopper, comfortable and the bike I use the most and simple, set up for Touring duties.
I ride tow paths, disused railways and tracks. Su suspension not needed.
Well I read that as you have one bike you find boring so should get shot of for starters, then you are only thinking about the three left...
That's how I deal with my inner hoarder when reducing stuff.. the first and last in the list you have identified yourself as the boring one with no implied sentimental aspect or rarity ( rare stuff is difficult to replace once its gone ) and the most useful one.. so my personal take as a professional hoarder would be decide which of the Roberts / Kona you want more and have a bike for short fun rides, sell one of them and treat the other with some choice bits etc to enjoy even more.
I got rid of a couple of mediocre bikes, a while ago and used the money to rebuild my own Kona Explosif with nos xt, hope hubbbed wheels, etc and its my short tiring pretend I am twenty bike.. no regrets here, its even better than before and I am not scared to ride it as hard as my wheezing lungs allow.
Ive now got various bikes but they include long held ambitions, my Kona Kileaua which would be about the last thing i would ever sell as ive had it 27 years and its a bit of a trophy job now underridden most certainly, Ive got my dads Marin ive built as a bike packer, horses for courses, if youve room. I also should point out the obvious benefit of multiple bikes is they dont wear out like when I had one bike in my teens, which adds to the enjoyment.
This one bike buisness is going to compromise what you have become accustomed too, whereas that looks like a list where reduction down to two could happen, and leave you with two very different bikes to enjoy. we all admire bikes, build and polish bikes on here, but ultimately it should be about enjoying riding them..!
Thats my take, but heads up dont tell anyone you wont buy more , as they always remember when they see you have bought another.. and point fingers and fun!